Publications
2020 |
Zhan, Wenqiang; Xiao, Changshi; Wen, Yuanqiao; Zhou, Chunhui; Yuan, Haiwen; Xiu, Supu; Zou, Xiong; Xie, Cheng; Li, Qiliang Adaptive Semantic Segmentation for Unmanned Surface Vehicle Navigation Journal Article ELECTRONICS, 9 (2), 2020. @article{ISI:000518412200013, title = {Adaptive Semantic Segmentation for Unmanned Surface Vehicle Navigation}, author = {Wenqiang Zhan and Changshi Xiao and Yuanqiao Wen and Chunhui Zhou and Haiwen Yuan and Supu Xiu and Xiong Zou and Cheng Xie and Qiliang Li}, doi = {10.3390/electronics9020213}, year = {2020}, date = {2020-02-01}, journal = {ELECTRONICS}, volume = {9}, number = {2}, publisher = {MDPI}, address = {ST ALBAN-ANLAGE 66, CH-4052 BASEL, SWITZERLAND}, abstract = {The intelligentization of unmanned surface vehicles (USVs) has recently attracted intensive interest. Visual perception of the water scenes is critical for the autonomous navigation of USVs. In this paper, an adaptive semantic segmentation method is proposed to recognize the water scenes. A semantic segmentation network model is designed to classify each pixel of an image into water, land or sky. The segmentation result is refined by the conditional random field (CRF) method. It is further improved accordingly by referring to the superpixel map. A weight map is generated based on the prediction confidence. The network trains itself with the refined pseudo label and the weight map. A set of experiments were designed to evaluate the proposed method. The experimental results show that the proposed method exhibits excellent performance with few-shot learning and is quite adaptable to a new environment, very efficient for limited manual labeled data utilization.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The intelligentization of unmanned surface vehicles (USVs) has recently attracted intensive interest. Visual perception of the water scenes is critical for the autonomous navigation of USVs. In this paper, an adaptive semantic segmentation method is proposed to recognize the water scenes. A semantic segmentation network model is designed to classify each pixel of an image into water, land or sky. The segmentation result is refined by the conditional random field (CRF) method. It is further improved accordingly by referring to the superpixel map. A weight map is generated based on the prediction confidence. The network trains itself with the refined pseudo label and the weight map. A set of experiments were designed to evaluate the proposed method. The experimental results show that the proposed method exhibits excellent performance with few-shot learning and is quite adaptable to a new environment, very efficient for limited manual labeled data utilization. |
Ye, Huixian; Shi, Chen; Li, Jiang; Tian, Li; Zeng, Min; Wang, Hui; Li, Qiliang New Alternating Current Noise Analytics Enables High Discrimination in Gas Sensing Journal Article ANALYTICAL CHEMISTRY, 92 (1), pp. 824-829, 2020, ISSN: 0003-2700. @article{ISI:000506719400071, title = {New Alternating Current Noise Analytics Enables High Discrimination in Gas Sensing}, author = {Huixian Ye and Chen Shi and Jiang Li and Li Tian and Min Zeng and Hui Wang and Qiliang Li}, doi = {10.1021/acs.analchem.9b03312}, issn = {0003-2700}, year = {2020}, date = {2020-01-01}, journal = {ANALYTICAL CHEMISTRY}, volume = {92}, number = {1}, pages = {824-829}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {Feature analysis has been increasingly considered as an important way to enhance the discrimination performance of gas sensors. In this work, a new analytical method based on alternating current noise spectrum is developed to discriminate chemically and structurally similar gases with remarkable performance. Compared with the conventional analytics based on the maximum, integral, and time of response, the noise spectrum of electrical response introduces a new informative feature to discriminate chemical gases. In experiment, three chemically and structurally similar gases, mesitylene, toluene, and o-xylene, are tested on ZnO thin film gas sensors. The result indicated that the noise analytics assisted by the support vector machine algorithm discriminated these similar gases with 94.2% in precision, about 20% higher than those alternating current noise analytics is very promising for application in sensorsobtained by conventional methods. Such a new for high discrimination precision.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Feature analysis has been increasingly considered as an important way to enhance the discrimination performance of gas sensors. In this work, a new analytical method based on alternating current noise spectrum is developed to discriminate chemically and structurally similar gases with remarkable performance. Compared with the conventional analytics based on the maximum, integral, and time of response, the noise spectrum of electrical response introduces a new informative feature to discriminate chemical gases. In experiment, three chemically and structurally similar gases, mesitylene, toluene, and o-xylene, are tested on ZnO thin film gas sensors. The result indicated that the noise analytics assisted by the support vector machine algorithm discriminated these similar gases with 94.2% in precision, about 20% higher than those alternating current noise analytics is very promising for application in sensorsobtained by conventional methods. Such a new for high discrimination precision. |
Ghimire, Nirmal J; Mazin, Igor I Topology and correlations on the kagome lattice Journal Article NATURE MATERIALS, 19 (2), pp. 137-138, 2020, ISSN: 1476-1122. @article{ISI:000511169400007, title = {Topology and correlations on the kagome lattice}, author = {Nirmal J Ghimire and Igor I Mazin}, doi = {10.1038/s41563-019-0589-8}, issn = {1476-1122}, year = {2020}, date = {2020-02-01}, journal = {NATURE MATERIALS}, volume = {19}, number = {2}, pages = {137-138}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Both a Dirac band and a flat band - signatures of topology and correlation - are found in a prototypical antiferromagnetic kagome lattice compound FeSn.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Both a Dirac band and a flat band - signatures of topology and correlation - are found in a prototypical antiferromagnetic kagome lattice compound FeSn. |
Walkup, Daniel; Ghahari, Fereshte; Gutierrez, Christopher; Watanabe, Kenji; Taniguchi, Takashi; Zhitenev, Nikolai B; Stroscio, Joseph A Tuning single-electron charging and interactions between compressible Landau level islands in graphene Journal Article PHYSICAL REVIEW B, 101 (3), 2020, ISSN: 2469-9950. @article{ISI:000510146500006, title = {Tuning single-electron charging and interactions between compressible Landau level islands in graphene}, author = {Daniel Walkup and Fereshte Ghahari and Christopher Gutierrez and Kenji Watanabe and Takashi Taniguchi and Nikolai B Zhitenev and Joseph A Stroscio}, doi = {10.1103/PhysRevB.101.035428}, issn = {2469-9950}, year = {2020}, date = {2020-01-01}, journal = {PHYSICAL REVIEW B}, volume = {101}, number = {3}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Interacting and tunable quantum dots (QDs) have been extensively exploited in condensed matter physics and quantum information science. Using a low-temperature scanning tunneling microscope (STM), we both create and directly image a new type of coupled QD system in graphene, a highly interacting quantum relativistic system with tunable density. Using detailed scanning tunneling spectroscopy (STS) measurements, we show that Landau quantization inside a potential well enables novel electron confinement via the incompressible strips between partially filled Landau levels (LLs), forming isolated and concentric LL QDs. By changing the charge density and the magnetic field we can tune continuously between single- and double-concentric LL QD systems within the same potential well. In the concentric QD regime, single-electron charging peaks of the two dots intersect, displaying a characteristic avoidance pattern. At moderate fields, we observe an unconventional avoidance pattern that differs significantly from that observed in capacitively coupled double-QD systems. We find that we can reproduce in detail this anomalous avoidance pattern within the framework of the electrostatic double-QD model by replacing the capacitive interdot coupling with a phenomenological charge-counting system in which charges in the inner concentric dot are counted in the total charge of both islands. The emergence of such strange forms of interdot coupling in a single potential well, together with the ease of producing such charge pockets in graphene and other two-dimensional (2D) materials, reveals an intriguing testbed for the confinement of 2D electrons in customizable potentials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Interacting and tunable quantum dots (QDs) have been extensively exploited in condensed matter physics and quantum information science. Using a low-temperature scanning tunneling microscope (STM), we both create and directly image a new type of coupled QD system in graphene, a highly interacting quantum relativistic system with tunable density. Using detailed scanning tunneling spectroscopy (STS) measurements, we show that Landau quantization inside a potential well enables novel electron confinement via the incompressible strips between partially filled Landau levels (LLs), forming isolated and concentric LL QDs. By changing the charge density and the magnetic field we can tune continuously between single- and double-concentric LL QD systems within the same potential well. In the concentric QD regime, single-electron charging peaks of the two dots intersect, displaying a characteristic avoidance pattern. At moderate fields, we observe an unconventional avoidance pattern that differs significantly from that observed in capacitively coupled double-QD systems. We find that we can reproduce in detail this anomalous avoidance pattern within the framework of the electrostatic double-QD model by replacing the capacitive interdot coupling with a phenomenological charge-counting system in which charges in the inner concentric dot are counted in the total charge of both islands. The emergence of such strange forms of interdot coupling in a single potential well, together with the ease of producing such charge pockets in graphene and other two-dimensional (2D) materials, reveals an intriguing testbed for the confinement of 2D electrons in customizable potentials. |
Oliver, Sean M; Young, Joshua; Krylyuk, Sergiy; Reinecke, Thomas L; Davydov, Albert V; Vora, Patrick M Valley phenomena in the candidate phase change material WSe2(1-x)Te2x Journal Article COMMUNICATIONS PHYSICS, 3 (1), 2020, ISSN: 2399-3650. @article{ISI:000510920900001, title = {Valley phenomena in the candidate phase change material WSe2(1-x)Te2x}, author = {Sean M Oliver and Joshua Young and Sergiy Krylyuk and Thomas L Reinecke and Albert V Davydov and Patrick M Vora}, doi = {10.1038/s42005-019-0277-7}, issn = {2399-3650}, year = {2020}, date = {2020-01-01}, journal = {COMMUNICATIONS PHYSICS}, volume = {3}, number = {1}, publisher = {NATURE PUBLISHING GROUP}, address = {MACMILLAN BUILDING, 4 CRINAN ST, LONDON N1 9XW, ENGLAND}, abstract = {Alloyed transition metal dichalcogenides provide a route toward atomically-thin phase change memories that host valleytronic behaviours. Here, Raman and photoluminescence spectroscopies are employed to demonstrate the robustness of valley polarisation to chemical substitution in monolayer alloys. Alloyed transition metal dichalcogenides provide an opportunity for coupling band engineering with valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe2(1-x)Te2x. Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe2 to the semimetallic 1T(d) phase of WTe2. We correlate these observations with density functional theory calculations and identify new Raman modes from W-Te vibrations in the 1H-phase alloy. Photoluminescence measurements show ultra-low energy emission features that highlight alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe2. These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Alloyed transition metal dichalcogenides provide a route toward atomically-thin phase change memories that host valleytronic behaviours. Here, Raman and photoluminescence spectroscopies are employed to demonstrate the robustness of valley polarisation to chemical substitution in monolayer alloys. Alloyed transition metal dichalcogenides provide an opportunity for coupling band engineering with valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe2(1-x)Te2x. Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe2 to the semimetallic 1T(d) phase of WTe2. We correlate these observations with density functional theory calculations and identify new Raman modes from W-Te vibrations in the 1H-phase alloy. Photoluminescence measurements show ultra-low energy emission features that highlight alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe2. These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices. |
2019 |
Chowdhury, Sugata; Hill, Heather; Simpson, Jeffrey; Vora, Patrick; Walker, Angela Hight; Tavazza, Francesca DFT analysis of Raman modes in the CDW states of layered 2H-TaSe2 and 2H-TaS2 Journal Article ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 257 , 2019, ISSN: 0065-7727, (National Meeting of the American-Chemical-Society (ACS), Orlando, FL, MAR 31-APR 04, 2019). @article{ISI:000478860505402, title = {DFT analysis of Raman modes in the CDW states of layered 2H-TaSe2 and 2H-TaS2}, author = {Sugata Chowdhury and Heather Hill and Jeffrey Simpson and Patrick Vora and Angela Hight Walker and Francesca Tavazza}, issn = {0065-7727}, year = {2019}, date = {2019-03-01}, journal = {ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY}, volume = {257}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, organization = {Amer Chem Soc}, note = {National Meeting of the American-Chemical-Society (ACS), Orlando, FL, MAR 31-APR 04, 2019}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Hu, Haiping; Huang, Biao; Zhao, Erhai; Liu, Vincent W Dynamical singularities of Floquet higher-order topological insulators Journal Article 2019. @article{Hu2019, title = {Dynamical singularities of Floquet higher-order topological insulators}, author = {Haiping Hu and Biao Huang and Erhai Zhao and Vincent W Liu}, url = {http://arxiv.org/abs/1905.03727}, year = {2019}, date = {2019-05-01}, abstract = {We propose a versatile framework to dynamically generate Floquet higher-order topological insulators by multi-step driving of topologically trivial Hamiltonians. Two analytically solvable examples are used to illustrate this procedure to yield Floquet quadrupole and octupole insulators with zero- and/or $backslashpi$-corner modes protected by mirror symmetries. We introduce dynamical topological invariants from the full unitary return map and show its phase bands contain Weyl singularities whose topological charges form dynamical multipole moments in the Brillouin zone. Combining them with the topological index of Floquet Hamiltonian gives a pair of $backslashmathbbZ_2$ invariant $backslashnu_0$ and $backslashnu_backslashpi$ which fully characterize the higher-order topology and predict the appearance of zero- and $backslashpi$-corner modes. Our work establishes a systematic route to construct and characterize Floquet higher-order topological phases.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We propose a versatile framework to dynamically generate Floquet higher-order topological insulators by multi-step driving of topologically trivial Hamiltonians. Two analytically solvable examples are used to illustrate this procedure to yield Floquet quadrupole and octupole insulators with zero- and/or $backslashpi$-corner modes protected by mirror symmetries. We introduce dynamical topological invariants from the full unitary return map and show its phase bands contain Weyl singularities whose topological charges form dynamical multipole moments in the Brillouin zone. Combining them with the topological index of Floquet Hamiltonian gives a pair of $backslashmathbbZ_2$ invariant $backslashnu_0$ and $backslashnu_backslashpi$ which fully characterize the higher-order topology and predict the appearance of zero- and $backslashpi$-corner modes. Our work establishes a systematic route to construct and characterize Floquet higher-order topological phases. |
Zou, Haiyuan; Zhao, Erhai; Guan, Xi-Wen; Liu, Vincent W Exactly Solvable Points and Symmetry Protected Topological Phases of Quantum Spins on a Zig-Zag Lattice Journal Article Physical Review Letters, 122 (18), pp. 180401, 2019, ISSN: 0031-9007. @article{Zou2019, title = {Exactly Solvable Points and Symmetry Protected Topological Phases of Quantum Spins on a Zig-Zag Lattice}, author = {Haiyuan Zou and Erhai Zhao and Xi-Wen Guan and Vincent W Liu}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.122.180401}, doi = {10.1103/PhysRevLett.122.180401}, issn = {0031-9007}, year = {2019}, date = {2019-05-01}, journal = {Physical Review Letters}, volume = {122}, number = {18}, pages = {180401}, abstract = {A large number of symmetry-protected topological (SPT) phases have been hypothesized for strongly interacting spin-1/2 systems in one dimension. Realizing these SPT phases, however, often demands fine-tunings hard to reach experimentally. And the lack of analytical solutions hinders the understanding of their many-body wave functions. Here we show that two kinds of SPT phases naturally arise for ultracold polar molecules confined in a zigzag optical lattice. This system, motivated by recent experiments, is described by a spin model whose exchange couplings can be tuned by an external field to reach parameter regions not studied before for spin chains or ladders. Within the enlarged parameter space, we find the ground state wave function can be obtained exactly along a line and at a special point, for these two phases respectively. These exact solutions provide a clear physical picture for the SPT phases and their edge excitations. We further obtain the phase diagram by using infinite time-evolving block decimation, and discuss the phase transitions between the two SPT phases and their experimental signatures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A large number of symmetry-protected topological (SPT) phases have been hypothesized for strongly interacting spin-1/2 systems in one dimension. Realizing these SPT phases, however, often demands fine-tunings hard to reach experimentally. And the lack of analytical solutions hinders the understanding of their many-body wave functions. Here we show that two kinds of SPT phases naturally arise for ultracold polar molecules confined in a zigzag optical lattice. This system, motivated by recent experiments, is described by a spin model whose exchange couplings can be tuned by an external field to reach parameter regions not studied before for spin chains or ladders. Within the enlarged parameter space, we find the ground state wave function can be obtained exactly along a line and at a special point, for these two phases respectively. These exact solutions provide a clear physical picture for the SPT phases and their edge excitations. We further obtain the phase diagram by using infinite time-evolving block decimation, and discuss the phase transitions between the two SPT phases and their experimental signatures. |
Shi, Chen; Rani, Asha; Thomson, Brian; Debnath, Ratan; Motayed, Abhishek; Ioannou, Dimitris E; Li, Qiliang High-performance room-temperature TiO2-functionalized GaN nanowire gas sensors Journal Article APPLIED PHYSICS LETTERS, 115 (12), 2019, ISSN: 0003-6951. @article{ISI:000487038900006, title = {High-performance room-temperature TiO2-functionalized GaN nanowire gas sensors}, author = {Chen Shi and Asha Rani and Brian Thomson and Ratan Debnath and Abhishek Motayed and Dimitris E Ioannou and Qiliang Li}, doi = {10.1063/1.5116677}, issn = {0003-6951}, year = {2019}, date = {2019-09-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {115}, number = {12}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {Hybrid gas sensors based on TiO2 functionalized gallium nitride nanowires have been prepared by nanofabrication and comprehensively studied for high-responsivity applications. The devices exhibited a high responsivity (25%) to 500 ppm NO2 assisted with ultraviolet illumination at room temperature. The thickness and doping concentration of TiO2 were engineered to improve the transducer function. The result indicated that an excellent n-type response can be stably obtained for a doping range from 1 x 10(17) cm(-3) to 1 x 10(19) cm(-3). The TiO2 thickness and doping concentration can be further fine-tuned to achieve optimal performance. In addition, a comprehensive device simulation was carried out to understand the device operation and gain insight for optimizing the device performance.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Hybrid gas sensors based on TiO2 functionalized gallium nitride nanowires have been prepared by nanofabrication and comprehensively studied for high-responsivity applications. The devices exhibited a high responsivity (25%) to 500 ppm NO2 assisted with ultraviolet illumination at room temperature. The thickness and doping concentration of TiO2 were engineered to improve the transducer function. The result indicated that an excellent n-type response can be stably obtained for a doping range from 1 x 10(17) cm(-3) to 1 x 10(19) cm(-3). The TiO2 thickness and doping concentration can be further fine-tuned to achieve optimal performance. In addition, a comprehensive device simulation was carried out to understand the device operation and gain insight for optimizing the device performance. |
Jiang, Kai; Pookpanratana, Sujitra J; Ren, Tong; Natoli, Sean N; Sperling, Brent A; Robertson, Joseph; Richter, Curt A; Yu, Sheng; Li, Qiliang Nonvolatile memory based on redox-active ruthenium molecular monolayers Journal Article APPLIED PHYSICS LETTERS, 115 (16), 2019, ISSN: 0003-6951. @article{ISI:000503750200015, title = {Nonvolatile memory based on redox-active ruthenium molecular monolayers}, author = {Kai Jiang and Sujitra J Pookpanratana and Tong Ren and Sean N Natoli and Brent A Sperling and Joseph Robertson and Curt A Richter and Sheng Yu and Qiliang Li}, doi = {10.1063/1.5108675}, issn = {0003-6951}, year = {2019}, date = {2019-10-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {115}, number = {16}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {A monolayer of diruthenium molecules was self-assembled onto the silicon oxide surface in a semiconductor capacitor structure with a ``click'' reaction for nonvolatile memory applications. The attachment of the active molecular monolayer was verified by x-ray photoelectron spectroscopy. The prototypical capacitor memory devices in this work employed a metal/oxide/molecule/oxide/Si structure. With the intrinsic redox-active charge-storage properties of diruthenium molecules, these capacitor memory devices exhibited fast Program and Erase speed, excellent endurance performance with negligible degradation of the memory window after 10(5) program/erase cycles, and very good 10-year memory retention. These experimental results indicate that the redox-active ruthenium molecular memory is very promising for use in nonvolatile memory applications. Published under license by AIP Publishing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A monolayer of diruthenium molecules was self-assembled onto the silicon oxide surface in a semiconductor capacitor structure with a ``click'' reaction for nonvolatile memory applications. The attachment of the active molecular monolayer was verified by x-ray photoelectron spectroscopy. The prototypical capacitor memory devices in this work employed a metal/oxide/molecule/oxide/Si structure. With the intrinsic redox-active charge-storage properties of diruthenium molecules, these capacitor memory devices exhibited fast Program and Erase speed, excellent endurance performance with negligible degradation of the memory window after 10(5) program/erase cycles, and very good 10-year memory retention. These experimental results indicate that the redox-active ruthenium molecular memory is very promising for use in nonvolatile memory applications. Published under license by AIP Publishing. |
Zhu, Hao; Richter, Curt A; Yu, Sheng; Ye, Huixian; Zeng, Min; Li, Qiliang Observation and control of the anomalous Aharonov-Bohm oscillation in enhanced-mode topological insulator nanowire field-effect transistors Journal Article APPLIED PHYSICS LETTERS, 115 (7), 2019, ISSN: 0003-6951. @article{ISI:000481469900038, title = {Observation and control of the anomalous Aharonov-Bohm oscillation in enhanced-mode topological insulator nanowire field-effect transistors}, author = {Hao Zhu and Curt A Richter and Sheng Yu and Huixian Ye and Min Zeng and Qiliang Li}, doi = {10.1063/1.5111180}, issn = {0003-6951}, year = {2019}, date = {2019-08-01}, journal = {APPLIED PHYSICS LETTERS}, volume = {115}, number = {7}, publisher = {AMER INST PHYSICS}, address = {1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA}, abstract = {Aharonov-Bohm (AB) oscillation is a quantum mechanical phenomenon which reveals the coupling of electromagnetic potentials with the electron wave function, affecting the phase of the wave function. Such a quantum interference effect can be demonstrated through the magnetotransport measurement focusing on low-dimensional electronic states. Here, we report the experimental observation of anomalous AB oscillation in an enhanced-mode topological insulator Bi2Se3 nanowire field-effect transistor (FET) under strong surface disorder, which is different from the reported AB oscillation in topological insulator nanostructures. The surrounding gate of the nanowire FET gives rise to tunability of the chemical potential and introduces strong disorder on the surface states, leading to primary oscillation with an anomalous h/e period. Furthermore, the oscillation exhibits a significant dependence on the gate voltage which has been preliminary explained with the quantization of the surface conduction channel. The experimental demonstration can be very attractive for further exploration of quantum phase interference through electrical approaches, enabling applications in future information and electromagnetic sensing technology.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Aharonov-Bohm (AB) oscillation is a quantum mechanical phenomenon which reveals the coupling of electromagnetic potentials with the electron wave function, affecting the phase of the wave function. Such a quantum interference effect can be demonstrated through the magnetotransport measurement focusing on low-dimensional electronic states. Here, we report the experimental observation of anomalous AB oscillation in an enhanced-mode topological insulator Bi2Se3 nanowire field-effect transistor (FET) under strong surface disorder, which is different from the reported AB oscillation in topological insulator nanostructures. The surrounding gate of the nanowire FET gives rise to tunability of the chemical potential and introduces strong disorder on the surface states, leading to primary oscillation with an anomalous h/e period. Furthermore, the oscillation exhibits a significant dependence on the gate voltage which has been preliminary explained with the quantization of the surface conduction channel. The experimental demonstration can be very attractive for further exploration of quantum phase interference through electrical approaches, enabling applications in future information and electromagnetic sensing technology. |
Keles, Ahmet; Zhao, Erhai; Li, Xiaopeng Phase diagram of Rydberg-dressed Fermi gas in two dimensions Journal Article 2019. @article{Keles2019a, title = {Phase diagram of Rydberg-dressed Fermi gas in two dimensions}, author = {Ahmet Keles and Erhai Zhao and Xiaopeng Li}, url = {http://arxiv.org/abs/1906.04235}, year = {2019}, date = {2019-06-01}, abstract = {Rydberg-dressed ultracold Fermi gas is one of the latest quantum many-body systems where the sign, strength, and range of the interaction can be controlled experimentally. The interaction in momentum space has a negative minimum at $q_c$ inversely proportional to the characteristic length-scale in real space, the soft-core radius $r_c$. We show theoretically that single-component (spinless) Rydberg-dressed Fermi gas in two dimensions has a rich phase diagram with novel superfluid and density wave orders due to the interplay of the Fermi momentum $p_F$, interaction range $r_c$, and interaction strength $u_0$. For repulsive bare interactions $u_0textgreater0$, the dominant instability is $f$-wave superfluid for $p_Fr_cbackslashlesssim 2$, and density wave for $p_Fr_cbackslashgtrsim 4$. The $f$-wave pairing in a repulsive Fermi gas is reminiscent of, but differs from, the conventional Kohn-Luttinger mechanism. For attractive bare interactions $u_0textless0$, the leading instability is $p$-wave pairing with double degeneracy, which points to a $p_x+ip_y$ topological superfluid. The phase diagram is obtained from functional renormalization group with high momentum resolution. It treats all competing many-body instabilities in the particle-particle and particle-hole channels on equal footing beyond leading order perturbation theory and random-phase approximation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Rydberg-dressed ultracold Fermi gas is one of the latest quantum many-body systems where the sign, strength, and range of the interaction can be controlled experimentally. The interaction in momentum space has a negative minimum at $q_c$ inversely proportional to the characteristic length-scale in real space, the soft-core radius $r_c$. We show theoretically that single-component (spinless) Rydberg-dressed Fermi gas in two dimensions has a rich phase diagram with novel superfluid and density wave orders due to the interplay of the Fermi momentum $p_F$, interaction range $r_c$, and interaction strength $u_0$. For repulsive bare interactions $u_0textgreater0$, the dominant instability is $f$-wave superfluid for $p_Fr_cbackslashlesssim 2$, and density wave for $p_Fr_cbackslashgtrsim 4$. The $f$-wave pairing in a repulsive Fermi gas is reminiscent of, but differs from, the conventional Kohn-Luttinger mechanism. For attractive bare interactions $u_0textless0$, the leading instability is $p$-wave pairing with double degeneracy, which points to a $p_x+ip_y$ topological superfluid. The phase diagram is obtained from functional renormalization group with high momentum resolution. It treats all competing many-body instabilities in the particle-particle and particle-hole channels on equal footing beyond leading order perturbation theory and random-phase approximation. |
Yu, Sheng; Tabibi, Bagher; Li, Qiliang; Seo, Felix Jaetae Piezoelectric enhancement of a defect-mediated boron nitride nanotube Journal Article JOURNAL OF PHYSICS D-APPLIED PHYSICS, 52 (33), 2019, ISSN: 0022-3727. @article{ISI:000471987400002, title = {Piezoelectric enhancement of a defect-mediated boron nitride nanotube}, author = {Sheng Yu and Bagher Tabibi and Qiliang Li and Felix Jaetae Seo}, doi = {10.1088/1361-6463/ab2582}, issn = {0022-3727}, year = {2019}, date = {2019-08-01}, journal = {JOURNAL OF PHYSICS D-APPLIED PHYSICS}, volume = {52}, number = {33}, publisher = {IOP PUBLISHING LTD}, address = {TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND}, abstract = {A zigzag boron nitride nanotube (ZBNNT) has a large intrinsic polarized dipole and a piezoelectric tunability with crystal chirality, nanotube diameter, and point defect. The piezoelectric coefficients (e(33)) of 8-ZBNNT with the VIA-group defects of S-N and Se-N are estimated to be 18.7 x 10(-2) C m(-2) and 14.9 x 10(-2) C m(-2), respectively. The coefficients of defect-mediated 8-ZBNNT are 97% and 57% bigger than that of pristine 8-ZBNNT. The elastic modulus of 8-ZBNNT is decreased due to the VIA-group defects, but is increased for the larger number of unit cells along zigzag rolling direction. The electronic band gap of 8-ZBNNT is reduced due to the VIA-group defects. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A zigzag boron nitride nanotube (ZBNNT) has a large intrinsic polarized dipole and a piezoelectric tunability with crystal chirality, nanotube diameter, and point defect. The piezoelectric coefficients (e(33)) of 8-ZBNNT with the VIA-group defects of S-N and Se-N are estimated to be 18.7 x 10(-2) C m(-2) and 14.9 x 10(-2) C m(-2), respectively. The coefficients of defect-mediated 8-ZBNNT are 97% and 57% bigger than that of pristine 8-ZBNNT. The elastic modulus of 8-ZBNNT is decreased due to the VIA-group defects, but is increased for the larger number of unit cells along zigzag rolling direction. The electronic band gap of 8-ZBNNT is reduced due to the VIA-group defects. The large piezoelectricity enhancement of 8-ZBNNT with VIA-group defect is attributable to the ionic contribution. Therefore, the unprecedented defect-mediated 8-ZBNNT provides a new material platform of mechanoelectronic devices for nanoscale sensors and energy conversions. |
Zhang, Kehao; Wang, Yuanxi; Joshi, Jaydeep; Zhang, Fu; Subramanian, Shruti; Terrones, Mauricio; Vora, Patrick; Crespi, Vincent; Robinson, Joshua A Probing the origin of lateral heterogeneities in synthetic monolayer molybdenum disulfide Journal Article 2D Materials, 6 (2), pp. 025008, 2019, ISSN: 2053-1583. @article{Zhang2019b, title = {Probing the origin of lateral heterogeneities in synthetic monolayer molybdenum disulfide}, author = {Kehao Zhang and Yuanxi Wang and Jaydeep Joshi and Fu Zhang and Shruti Subramanian and Mauricio Terrones and Patrick Vora and Vincent Crespi and Joshua A Robinson}, url = {http://iopscience.iop.org/article/10.1088/2053-1583/aafd9a http://stacks.iop.org/2053-1583/6/i=2/a=025008?key=crossref.006e7cddfc7a7f13021280ae38e90026}, doi = {10.1088/2053-1583/aafd9a}, issn = {2053-1583}, year = {2019}, date = {2019-02-01}, journal = {2D Materials}, volume = {6}, number = {2}, pages = {025008}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Keleş, Ahmet; Zhao, Erhai; Liu, Vincent W Scrambling dynamics and many-body chaos in a random dipolar spin model Journal Article Physical Review A, 99 (5), pp. 053620, 2019, ISSN: 2469-9926. @article{Keles2019b, title = {Scrambling dynamics and many-body chaos in a random dipolar spin model}, author = {Ahmet Kele\c{s} and Erhai Zhao and Vincent W Liu}, url = {https://link.aps.org/doi/10.1103/PhysRevA.99.053620}, doi = {10.1103/PhysRevA.99.053620}, issn = {2469-9926}, year = {2019}, date = {2019-05-01}, journal = {Physical Review A}, volume = {99}, number = {5}, pages = {053620}, abstract = {Is there a quantum many-body system that scrambles information as fast as a black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for chaos, but it requires random all-to-all couplings of Majorana fermions that are hard to realize in experiments. Here we examine a quantum spin model of randomly oriented dipoles where the spin exchange is governed by dipole-dipole interactions. The model is inspired by recent experiments on dipolar spin systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We map out the phase diagram of this model by computing the energy level statistics, spectral form factor, and out-of-time-order correlation (OTOC) functions. We find a broad regime of many-body chaos where the energy levels obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at different times: Its early-time dynamics is characterized by an exponential growth, while the approach to its saturated value at late times obeys a power law. The temperature scaling of the Lyapunov exponent $backslashlambda_L$ shows that while it is well below the conjectured bound $2backslashpi T$ at high temperatures, $backslashlambda_L$ approaches the bound at low temperatures and for large number of spins.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Is there a quantum many-body system that scrambles information as fast as a black hole? The Sachev-Ye-Kitaev model can saturate the conjectured bound for chaos, but it requires random all-to-all couplings of Majorana fermions that are hard to realize in experiments. Here we examine a quantum spin model of randomly oriented dipoles where the spin exchange is governed by dipole-dipole interactions. The model is inspired by recent experiments on dipolar spin systems of magnetic atoms, dipolar molecules, and nitrogen-vacancy centers. We map out the phase diagram of this model by computing the energy level statistics, spectral form factor, and out-of-time-order correlation (OTOC) functions. We find a broad regime of many-body chaos where the energy levels obey Wigner-Dyson statistics and the OTOC shows distinctive behaviors at different times: Its early-time dynamics is characterized by an exponential growth, while the approach to its saturated value at late times obeys a power law. The temperature scaling of the Lyapunov exponent $backslashlambda_L$ shows that while it is well below the conjectured bound $2backslashpi T$ at high temperatures, $backslashlambda_L$ approaches the bound at low temperatures and for large number of spins. |
Joshi, Jaydeep; Hill, Heather M; Chowdhury, Sugata; Malliakas, Christos D; Tavazza, Francesca; Chatterjee, Utpal; Walker, Angela Hight R; Vora, Patrick M Short-range charge density wave order in 2H-TaS2 Journal Article PHYSICAL REVIEW B, 99 (24), 2019, ISSN: 2469-9950. @article{ISI:000473018900001, title = {Short-range charge density wave order in 2H-TaS2}, author = {Jaydeep Joshi and Heather M Hill and Sugata Chowdhury and Christos D Malliakas and Francesca Tavazza and Utpal Chatterjee and Angela Hight R Walker and Patrick M Vora}, doi = {10.1103/PhysRevB.99.245144}, issn = {2469-9950}, year = {2019}, date = {2019-06-01}, journal = {PHYSICAL REVIEW B}, volume = {99}, number = {24}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {2H-TaS2 undergoes a charge density wave (CDW) transition at T-CDW similar to 75 K, however key questions regarding the onset of CDWorder remain under debate. In this study, we explore the CDWtransition through a combination of temperature and excitation-dependent Raman spectroscopy, angle resolved photoemission spectroscopy (ARPES), and density functional theory (DFT). Below T-CDW we identify two CDW amplitude modes that redshift and broaden with increasing temperature and one zone-folded mode that disappears above T-CDW. Above T-CDW, we observe a strong two-phonon mode that softens substantially upon cooling, which suggests the presence of substantial lattice distortions at temperatures as high as 250 K. This correlates with the ARPES observation of the persistence of a CDW energy gap above T-CDW and finite-temperature DFT calculations of the phonon band structure that indicate an instability occurring well above the CDW transition temperature. DFT also provides the atomic displacements of the CDW amplitude modes and reproduces their temperature dependence. From these observations we suggest that short range CDW order exists well above T-CDW, which poses new questions regarding the interplay between electronic structure and vibrational modes in layered CDW materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } 2H-TaS2 undergoes a charge density wave (CDW) transition at T-CDW similar to 75 K, however key questions regarding the onset of CDWorder remain under debate. In this study, we explore the CDWtransition through a combination of temperature and excitation-dependent Raman spectroscopy, angle resolved photoemission spectroscopy (ARPES), and density functional theory (DFT). Below T-CDW we identify two CDW amplitude modes that redshift and broaden with increasing temperature and one zone-folded mode that disappears above T-CDW. Above T-CDW, we observe a strong two-phonon mode that softens substantially upon cooling, which suggests the presence of substantial lattice distortions at temperatures as high as 250 K. This correlates with the ARPES observation of the persistence of a CDW energy gap above T-CDW and finite-temperature DFT calculations of the phonon band structure that indicate an instability occurring well above the CDW transition temperature. DFT also provides the atomic displacements of the CDW amplitude modes and reproduces their temperature dependence. From these observations we suggest that short range CDW order exists well above T-CDW, which poses new questions regarding the interplay between electronic structure and vibrational modes in layered CDW materials. |
Vora, Patrick M; Bracker, Allan S; Carter, Samuel G; Kim, Mijin; Kim, Chul Soo; Gammon, Daniel Strong coupling of a quantum dot molecule to a photonic crystal cavity Journal Article Physical Review B, 99 (16), pp. 165420, 2019, ISSN: 2469-9950. @article{Vora2019, title = {Strong coupling of a quantum dot molecule to a photonic crystal cavity}, author = {Patrick M Vora and Allan S Bracker and Samuel G Carter and Mijin Kim and Chul Soo Kim and Daniel Gammon}, url = {https://link.aps.org/doi/10.1103/PhysRevB.99.165420}, doi = {10.1103/PhysRevB.99.165420}, issn = {2469-9950}, year = {2019}, date = {2019-04-01}, journal = {Physical Review B}, volume = {99}, number = {16}, pages = {165420}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Ansari, Jaafar N; Sauer, Karen L; Glasbrenner, James K The Predictive Power of Different Projector-Augmented Wave Potentials for Nuclear Quadrupole Resonance Journal Article CRYSTALS, 9 (10), 2019, ISSN: 2073-4352. @article{ISI:000498263500022, title = {The Predictive Power of Different Projector-Augmented Wave Potentials for Nuclear Quadrupole Resonance}, author = {Jaafar N Ansari and Karen L Sauer and James K Glasbrenner}, doi = {10.3390/cryst9100507}, issn = {2073-4352}, year = {2019}, date = {2019-10-01}, journal = {CRYSTALS}, volume = {9}, number = {10}, publisher = {MDPI}, address = {ST ALBAN-ANLAGE 66, CH-4052 BASEL, SWITZERLAND}, abstract = {The projector-augmented wave (PAW) method is used to calculate electric field gradients (EFG) for various PAW potentials. A variety of crystals containing reactive nonmetal, simple metal, and transition elements, are evaluated in order to determine the predictive ability of the PAW method for the determination of nuclear quadrupole resonance frequencies in previously unstudied materials and their polymorphs. All results were compared to experimental results and, where possible, to previous density functional theory (DFT) calculations. The EFG at the N-14 site of NaNO2 is calculated by DFT for the first time. The reactive nonmetal elements were not very sensitive to the variation in PAW potentials, and calculations were quite close to experimental values. For the other elements, the various PAW potentials led to a clear spread in EFG values, with no one universal potential emerging. Within the spread, there was agreement with other ab initio models.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The projector-augmented wave (PAW) method is used to calculate electric field gradients (EFG) for various PAW potentials. A variety of crystals containing reactive nonmetal, simple metal, and transition elements, are evaluated in order to determine the predictive ability of the PAW method for the determination of nuclear quadrupole resonance frequencies in previously unstudied materials and their polymorphs. All results were compared to experimental results and, where possible, to previous density functional theory (DFT) calculations. The EFG at the N-14 site of NaNO2 is calculated by DFT for the first time. The reactive nonmetal elements were not very sensitive to the variation in PAW potentials, and calculations were quite close to experimental values. For the other elements, the various PAW potentials led to a clear spread in EFG values, with no one universal potential emerging. Within the spread, there was agreement with other ab initio models. |
Takeda, H; Yasuoka, H; Yoshida, M; Takigawa, M; Ghimire, N J; Mandrus, D; Sales, B C V-51-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8 Journal Article PHYSICAL REVIEW B, 100 (5), 2019, ISSN: 2469-9950. @article{ISI:000478991000003, title = {V-51-NMR study on the S=1/2 square lattice antiferromagnet K2V3O8}, author = {H Takeda and H Yasuoka and M Yoshida and M Takigawa and N J Ghimire and D Mandrus and B C Sales}, doi = {10.1103/PhysRevB.100.054406}, issn = {2469-9950}, year = {2019}, date = {2019-08-01}, journal = {PHYSICAL REVIEW B}, volume = {100}, number = {5}, publisher = {AMER PHYSICAL SOC}, address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, abstract = {Static and dynamic properties of the quasi-two-dimensional antiferromagnet K2V3O8 have been investigated by V-51-NMR experiments on nonmagnetic V5+ sites. Above the structural transition temperature T-S = 115 K, NMR spectra are fully compatible with the P4bm space-group symmetry. The formation of superstructure below T-S causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along the c axis below the magnetic transition temperature T-N similar to 4 K is qualitatively consistent with a simple Neel order and a spin-flop transition. However, a broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate 1/T-1 below T-N shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V5+ and magnetic V4+ sites. The results indicate strong gapless spin fluctuations, which could arise from incommensurate orders or complex spin textures.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Static and dynamic properties of the quasi-two-dimensional antiferromagnet K2V3O8 have been investigated by V-51-NMR experiments on nonmagnetic V5+ sites. Above the structural transition temperature T-S = 115 K, NMR spectra are fully compatible with the P4bm space-group symmetry. The formation of superstructure below T-S causes splitting of the NMR lines, which get broadened at lower temperatures so that individual peaks are not well resolved. Evolution of NMR spectra with magnetic field along the c axis below the magnetic transition temperature T-N similar to 4 K is qualitatively consistent with a simple Neel order and a spin-flop transition. However, a broad feature of the spectra does not rule out possible incommensurate spin structure. The spin-lattice relaxation rate 1/T-1 below T-N shows huge enhancement for a certain range of magnetic field, which is independent of temperature and attributed to cross relaxation due to anomalously large nuclear spin-spin coupling between V5+ and magnetic V4+ sites. The results indicate strong gapless spin fluctuations, which could arise from incommensurate orders or complex spin textures. |
Oliver, Sean M; Young, Joshua; Krylyuk, Sergiy; Reinecke, Thomas L; Davydov, Albert V; Vora, Patrick M Valley Phenomena in the Candidate Phase Change Material WSe$_2(1-x)$Te$_2x$ Journal Article 2019. @article{Oliver2019, title = {Valley Phenomena in the Candidate Phase Change Material WSe$_2(1-x)$Te$_2x$}, author = {Sean M Oliver and Joshua Young and Sergiy Krylyuk and Thomas L Reinecke and Albert V Davydov and Patrick M Vora}, url = {http://arxiv.org/abs/1908.00506}, year = {2019}, date = {2019-08-01}, abstract = {Alloyed transition metal dichalcogenides provide a unique opportunity for coupling band engineering and valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe$_2(1-x)$Te$_2x$. Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe$_2$ to the semimetallic 1T$_d$ phase of WTe$_2$. We correlate these observations with density functional theory calculations and identify new Raman modes from 1H-WTe$_2$. Photoluminescence measurements show ultra-low energy emission features that highlight the presence of significant alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe$_2$. These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Alloyed transition metal dichalcogenides provide a unique opportunity for coupling band engineering and valleytronic phenomena in an atomically-thin platform. However, valley properties in alloys remain largely unexplored. We investigate the valley degree of freedom in monolayer alloys of the phase change candidate material WSe$_2(1-x)$Te$_2x$. Low temperature Raman measurements track the alloy-induced transition from the semiconducting 1H phase of WSe$_2$ to the semimetallic 1T$_d$ phase of WTe$_2$. We correlate these observations with density functional theory calculations and identify new Raman modes from 1H-WTe$_2$. Photoluminescence measurements show ultra-low energy emission features that highlight the presence of significant alloy disorder arising from the large W-Te bond lengths. Interestingly, valley polarization and coherence in alloys survive at high Te compositions and are more robust against temperature than in WSe$_2$. These findings illustrate the persistence of valley properties in alloys with highly dissimilar parent compounds and suggest band engineering can be utilized for valleytronic devices. |
2018 |
Keleş, Ahmet; Zhao, Erhai Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions Journal Article Physical Review Letters, 120 (18), pp. 187202, 2018, ISSN: 0031-9007. @article{PhysRevLett.120.187202, title = {Absence of Long-Range Order in a Triangular Spin System with Dipolar Interactions}, author = {Ahmet Kele\c{s} and Erhai Zhao}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.187202}, doi = {10.1103/PhysRevLett.120.187202}, issn = {0031-9007}, year = {2018}, date = {2018-05-01}, journal = {Physical Review Letters}, volume = {120}, number = {18}, pages = {187202}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Zhao, K; Glasbrenner, J K; Gretarsson, H; Schmitz, D; Bednarcik, J; Etter, M; Sun, J P; Manna, R S; Al-Zein, A; Lafuerza, S; Scherer, W; Cheng, J G; Gegenwart, P Physical Review B, 97 (2), pp. 020510, 2018, ISSN: 2469-9950. @article{Zhao2018_PRBRC_Collapsed, title = {Collapsed tetragonal phase as a strongly covalent and fully nonmagnetic state: Persistent magnetism with interlayer As\textendashAs bond formation in Rh-doped Ca0.8 Sr0.2 Fe2 As2}, author = {K Zhao and J K Glasbrenner and H Gretarsson and D Schmitz and J Bednarcik and M Etter and J P Sun and R S Manna and A Al-Zein and S Lafuerza and W Scherer and J G Cheng and P Gegenwart}, url = {https://link.aps.org/doi/10.1103/PhysRevB.97.020510}, doi = {10.1103/PhysRevB.97.020510}, issn = {2469-9950}, year = {2018}, date = {2018-01-01}, journal = {Physical Review B}, volume = {97}, number = {2}, pages = {020510}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Díaz, Sebastián A; Oliver, Sean M; Hastman, David A; Medintz, Igor L; Vora, Patrick M Increased Transfer Efficiency from Molecular Photonic Wires on Solid Substrates and Cryogenic Conditions Journal Article The Journal of Physical Chemistry Letters, 9 (13), pp. 3654–3659, 2018, ISSN: 1948-7185. @article{Diaz2018, title = {Increased Transfer Efficiency from Molecular Photonic Wires on Solid Substrates and Cryogenic Conditions}, author = {Sebasti\'{a}n A D\'{i}az and Sean M Oliver and David A Hastman and Igor L Medintz and Patrick M Vora}, url = {http://pubs.acs.org/doi/10.1021/acs.jpclett.8b00931}, doi = {10.1021/acs.jpclett.8b00931}, issn = {1948-7185}, year = {2018}, date = {2018-07-01}, journal = {The Journal of Physical Chemistry Letters}, volume = {9}, number = {13}, pages = {3654--3659}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Díaz, Sebastián A; Oliver, Sean M; Hastman, David A; Medintz, Igor L; Vora, Patrick M Increased Transfer Efficiency from Molecular Photonic Wires on Solid Substrates and Cryogenic Conditions Journal Article The Journal of Physical Chemistry Letters, 9 (13), pp. 3654–3659, 2018, ISSN: 1948-7185. @article{Diaz2018b, title = {Increased Transfer Efficiency from Molecular Photonic Wires on Solid Substrates and Cryogenic Conditions}, author = {Sebasti\'{a}n A D\'{i}az and Sean M Oliver and David A Hastman and Igor L Medintz and Patrick M Vora}, url = {http://pubs.acs.org/doi/10.1021/acs.jpclett.8b00931}, doi = {10.1021/acs.jpclett.8b00931}, issn = {1948-7185}, year = {2018}, date = {2018-07-01}, journal = {The Journal of Physical Chemistry Letters}, volume = {9}, number = {13}, pages = {3654--3659}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Kang, Pilgyu; Kim, Kyoung-Ho; Park, Hong-Gyu; Nam, SungWoo Mechanically reconfigurable architectured graphene for tunable plasmonic resonances Journal Article Light: Science & Applications, 7 (1), pp. 17, 2018, ISSN: 2047-7538. @article{Kang2018a, title = {Mechanically reconfigurable architectured graphene for tunable plasmonic resonances}, author = {Pilgyu Kang and Kyoung-Ho Kim and Hong-Gyu Park and SungWoo Nam}, url = {http://www.nature.com/articles/s41377-018-0002-4}, doi = {10.1038/s41377-018-0002-4}, issn = {2047-7538}, year = {2018}, date = {2018-12-01}, journal = {Light: Science & Applications}, volume = {7}, number = {1}, pages = {17}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Vega, Devin; Tian, Mingzhen Photon echoes from an atomic frequency comb affected by population relaxation Journal Article Physical Review A, 98 (5), pp. 052340, 2018, ISSN: 2469-9926. @article{Vega2018a, title = {Photon echoes from an atomic frequency comb affected by population relaxation}, author = {Devin Vega and Mingzhen Tian}, url = {https://link.aps.org/doi/10.1103/PhysRevA.98.052340}, doi = {10.1103/PhysRevA.98.052340}, issn = {2469-9926}, year = {2018}, date = {2018-11-01}, journal = {Physical Review A}, volume = {98}, number = {5}, pages = {052340}, abstract = {textcopyright 2018 American Physical Society. The atomic frequency comb (AFC) is a promising approach for quantum memory, yet creating an ideal AFC only in the ground-state population remains a challenge. We studied an imperfect AFC initially created in the population inversion between the excited and ground states and redistributed due to population relaxation in a three-level system where a long-lived metastable state plays a crucial role. A theoretical model has been developed to treat the storage of a weak input pulse and retrieval in the form of a photon echo. By comparing theory with experimental results we have studied the echo efficiency and overall attenuation of an input pulse in the AFC affected by both its initial spectral structure and the population relaxation.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright 2018 American Physical Society. The atomic frequency comb (AFC) is a promising approach for quantum memory, yet creating an ideal AFC only in the ground-state population remains a challenge. We studied an imperfect AFC initially created in the population inversion between the excited and ground states and redistributed due to population relaxation in a three-level system where a long-lived metastable state plays a crucial role. A theoretical model has been developed to treat the storage of a weak input pulse and retrieval in the form of a photon echo. By comparing theory with experimental results we have studied the echo efficiency and overall attenuation of an input pulse in the AFC affected by both its initial spectral structure and the population relaxation. |
Keleş, Ahmet; Zhao, Erhai Renormalization group analysis of dipolar Heisenberg model on square lattice Journal Article Physical Review B, 97 (24), pp. 245105, 2018, ISSN: 2469-9950. @article{PhysRevB.97.245105, title = {Renormalization group analysis of dipolar Heisenberg model on square lattice}, author = {Ahmet Kele\c{s} and Erhai Zhao}, url = {https://link.aps.org/doi/10.1103/PhysRevB.97.245105}, doi = {10.1103/PhysRevB.97.245105}, issn = {2469-9950}, year = {2018}, date = {2018-06-01}, journal = {Physical Review B}, volume = {97}, number = {24}, pages = {245105}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Cooper, Robert J; Prescott, David W; Lee, Garrett J; Sauer, Karen L RF atomic magnetometer array with over 40 dB interference suppression using electron spin resonance Journal Article Journal of Magnetic Resonance, 2018, ISSN: 10907807. @article{COOPER2018, title = {RF atomic magnetometer array with over 40 dB interference suppression using electron spin resonance}, author = {Robert J Cooper and David W Prescott and Garrett J Lee and Karen L Sauer}, url = {http://www.sciencedirect.com/science/article/pii/S1090780718302118 https://linkinghub.elsevier.com/retrieve/pii/S1090780718302118}, doi = {10.1016/j.jmr.2018.08.007}, issn = {10907807}, year = {2018}, date = {2018-08-01}, journal = {Journal of Magnetic Resonance}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Zhang, Kehao; Bersch, Brian M; Joshi, Jaydeep; Addou, Rafik; Cormier, Christopher R; Zhang, Chenxi; Xu, Ke; Briggs, Natalie C; Wang, Ke; Subramanian, Shruti; Cho, Kyeongjae; Fullerton-Shirey, Susan; Wallace, Robert M; Vora, Patrick M; Robinson, Joshua A Tuning the Electronic and Photonic Properties of Monolayer MoS 2 via In Situ Rhenium Substitutional Doping Journal Article Advanced Functional Materials, 28 (16), pp. 1706950, 2018, ISSN: 1616301X. @article{Zhang2018db, title = {Tuning the Electronic and Photonic Properties of Monolayer MoS 2 via In Situ Rhenium Substitutional Doping}, author = {Kehao Zhang and Brian M Bersch and Jaydeep Joshi and Rafik Addou and Christopher R Cormier and Chenxi Zhang and Ke Xu and Natalie C Briggs and Ke Wang and Shruti Subramanian and Kyeongjae Cho and Susan Fullerton-Shirey and Robert M Wallace and Patrick M Vora and Joshua A Robinson}, url = {http://doi.wiley.com/10.1002/adfm.201706950}, doi = {10.1002/adfm.201706950}, issn = {1616301X}, year = {2018}, date = {2018-04-01}, journal = {Advanced Functional Materials}, volume = {28}, number = {16}, pages = {1706950}, abstract = {textcopyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS 2 ) and tungsten (W) doping of molybdenum diselenide (MoSe 2 ) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS 2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the Mo-O bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS 2 is a promising route toward electronic and photonic engineering of 2D materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS 2 ) and tungsten (W) doping of molybdenum diselenide (MoSe 2 ) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS 2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the Mo-O bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS 2 is a promising route toward electronic and photonic engineering of 2D materials. |
Zhang, Kehao; Bersch, Brian M; Joshi, Jaydeep; Addou, Rafik; Cormier, Christopher R; Zhang, Chenxi; Xu, Ke; Briggs, Natalie C; Wang, Ke; Subramanian, Shruti; Cho, Kyeongjae; Fullerton-Shirey, Susan; Wallace, Robert M; Vora, Patrick M; Robinson, Joshua A Tuning the Electronic and Photonic Properties of Monolayer MoS2 via In Situ Rhenium Substitutional Doping Journal Article Advanced Functional Materials, 28 (16), pp. 1706950, 2018, ISSN: 1616301X. @article{Zhang2018d, title = {Tuning the Electronic and Photonic Properties of Monolayer MoS2 via In Situ Rhenium Substitutional Doping}, author = {Kehao Zhang and Brian M Bersch and Jaydeep Joshi and Rafik Addou and Christopher R Cormier and Chenxi Zhang and Ke Xu and Natalie C Briggs and Ke Wang and Shruti Subramanian and Kyeongjae Cho and Susan Fullerton-Shirey and Robert M Wallace and Patrick M Vora and Joshua A Robinson}, url = {http://doi.wiley.com/10.1002/adfm.201706950}, doi = {10.1002/adfm.201706950}, issn = {1616301X}, year = {2018}, date = {2018-04-01}, journal = {Advanced Functional Materials}, volume = {28}, number = {16}, pages = {1706950}, abstract = {textcopyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS 2 ) and tungsten (W) doping of molybdenum diselenide (MoSe 2 ) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS 2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the Mo-O bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS 2 is a promising route toward electronic and photonic engineering of 2D materials.}, keywords = {}, pubstate = {published}, tppubtype = {article} } textcopyright 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Doping is a fundamental requirement for tuning and improving the properties of conventional semiconductors. Recent doping studies including niobium (Nb) doping of molybdenum disulfide (MoS 2 ) and tungsten (W) doping of molybdenum diselenide (MoSe 2 ) have suggested that substitutional doping may provide an efficient route to tune the doping type and suppress deep trap levels of 2D materials. To date, the impact of the doping on the structural, electronic, and photonic properties of in situ-doped monolayers remains unanswered due to challenges including strong film substrate charge transfer, and difficulty achieving doping concentrations greater than 0.3 at%. Here, in situ rhenium (Re) doping of synthetic monolayer MoS 2 with ≈1 at% Re is demonstrated. To limit substrate film charge transfer, r-plane sapphire is used. Electronic measurements demonstrate that 1 at% Re doping achieves nearly degenerate n-type doping, which agrees with density functional theory calculations. Moreover, low-temperature photoluminescence indicates a significant quench of the defect-bound emission when Re is introduced, which is attributed to the Mo-O bond and sulfur vacancies passivation and reduction in gap states due to the presence of Re. The work presented here demonstrates that Re doping of MoS 2 is a promising route toward electronic and photonic engineering of 2D materials. |
Keles, Ahmet; Zhao, Erhai Weyl nodes in periodic structures of superconductors and spin-active materials Journal Article Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 376 (2125), pp. 20150151, 2018, ISSN: 1364-503X. @article{Keles2018, title = {Weyl nodes in periodic structures of superconductors and spin-active materials}, author = {Ahmet Keles and Erhai Zhao}, url = {https://doi.org/10.1098/rsta.2015.0151 http://rsta.royalsocietypublishing.org/lookup/doi/10.1098/rsta.2015.0151}, doi = {10.1098/rsta.2015.0151}, issn = {1364-503X}, year = {2018}, date = {2018-08-01}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {376}, number = {2125}, pages = {20150151}, publisher = {The Royal Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
2017 |
Kim, Minsu; Kang, Pilgyu; Leem, Juyoung; Nam, SungWoo A stretchable crumpled graphene photodetector with plasmonically enhanced photoresponsivity Journal Article Nanoscale, 9 (12), pp. 4058–4065, 2017, ISSN: 2040-3364. @article{Kim2017c, title = {A stretchable crumpled graphene photodetector with plasmonically enhanced photoresponsivity}, author = {Minsu Kim and Pilgyu Kang and Juyoung Leem and SungWoo Nam}, url = {http://xlink.rsc.org/?DOI=C6NR09338H}, doi = {10.1039/C6NR09338H}, issn = {2040-3364}, year = {2017}, date = {2017-01-01}, journal = {Nanoscale}, volume = {9}, number = {12}, pages = {4058--4065}, abstract = {Graphene has been widely explored for flexible, high-performance photodetectors due to its exceptional mechanical strength, broadband absorption, and high carrier mobility. However, the low stretchability and limited photoabsorption of graphene have restricted its applications in flexible and highly sensitive photodetection systems. Various hybrid systems based on photonic or plasmonic nanostructures have been introduced to improve the limited photoresponsivity of graphene photodetectors. In most cases, the hybrid systems succeeded in the enhancement of photoresponsivity, but showed limited mechanical stretchability. Here, we demonstrate a stretchable photodetector based on a crumpled graphene\textendashgold nanoparticle (AuNP) hybrid structure with ∼1200% enhanced photoresponsivity, compared to a conventional flat graphene-only photodetector, and exceptional mechanical stretchability up to a 200% tensile strain. We achieve plasmonically enhanced photoresponsivity by integrating AuNPs with graphene. By crumpling the hybrid structure, we realize mechanical stretchability and further enhancement of the optical absorption by densification. We also demonstrate that our highly stretchable photodetector with enhanced photoresponsivity can be integrated on a contact lens and a spring structure. We believe that our stretchable, high performance graphene photodetector can find broad applications for conformable and flexible optical sensors and dynamic mechanical strain sensors.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Graphene has been widely explored for flexible, high-performance photodetectors due to its exceptional mechanical strength, broadband absorption, and high carrier mobility. However, the low stretchability and limited photoabsorption of graphene have restricted its applications in flexible and highly sensitive photodetection systems. Various hybrid systems based on photonic or plasmonic nanostructures have been introduced to improve the limited photoresponsivity of graphene photodetectors. In most cases, the hybrid systems succeeded in the enhancement of photoresponsivity, but showed limited mechanical stretchability. Here, we demonstrate a stretchable photodetector based on a crumpled graphene–gold nanoparticle (AuNP) hybrid structure with ∼1200% enhanced photoresponsivity, compared to a conventional flat graphene-only photodetector, and exceptional mechanical stretchability up to a 200% tensile strain. We achieve plasmonically enhanced photoresponsivity by integrating AuNPs with graphene. By crumpling the hybrid structure, we realize mechanical stretchability and further enhancement of the optical absorption by densification. We also demonstrate that our highly stretchable photodetector with enhanced photoresponsivity can be integrated on a contact lens and a spring structure. We believe that our stretchable, high performance graphene photodetector can find broad applications for conformable and flexible optical sensors and dynamic mechanical strain sensors. |
Keleş, Ahmet; Zhao, Erhai; Liu, Vincent W Effective theory of interacting fermions in shaken square optical lattices Journal Article Physical Review A, 95 (6), pp. 063619, 2017, ISSN: 2469-9926. @article{PhysRevA.95.063619, title = {Effective theory of interacting fermions in shaken square optical lattices}, author = {Ahmet Kele\c{s} and Erhai Zhao and Vincent W Liu}, url = {https://link.aps.org/doi/10.1103/PhysRevA.95.063619 http://link.aps.org/doi/10.1103/PhysRevA.95.063619}, doi = {10.1103/PhysRevA.95.063619}, issn = {2469-9926}, year = {2017}, date = {2017-06-01}, journal = {Physical Review A}, volume = {95}, number = {6}, pages = {063619}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Zou, Haiyuan; Zhao, Erhai; Liu, Vincent W Frustrated Magnetism of Dipolar Molecules on a Square Optical Lattice: Prediction of a Quantum Paramagnetic Ground State Journal Article Physical Review Letters, 119 (5), pp. 050401, 2017, ISSN: 0031-9007. @article{PhysRevLett.119.050401, title = {Frustrated Magnetism of Dipolar Molecules on a Square Optical Lattice: Prediction of a Quantum Paramagnetic Ground State}, author = {Haiyuan Zou and Erhai Zhao and Vincent W Liu}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.119.050401 http://link.aps.org/doi/10.1103/PhysRevLett.119.050401}, doi = {10.1103/PhysRevLett.119.050401}, issn = {0031-9007}, year = {2017}, date = {2017-07-01}, journal = {Physical Review Letters}, volume = {119}, number = {5}, pages = {050401}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Wang, Michael Cai; Leem, Juyoung; Kang, Pilgyu; Choi, Jonghyun; Knapp, Peter; Yong, Keong; Nam, SungWoo Mechanical instability driven self-assembly and architecturing of 2D materials Journal Article 2D Materials, 4 (2), pp. 022002, 2017, ISSN: 2053-1583. @article{Wang2017e, title = {Mechanical instability driven self-assembly and architecturing of 2D materials}, author = {Michael Cai Wang and Juyoung Leem and Pilgyu Kang and Jonghyun Choi and Peter Knapp and Keong Yong and SungWoo Nam}, url = {http://stacks.iop.org/2053-1583/4/i=2/a=022002?key=crossref.f4723d0c820bc3cf2650ad83fec550c1}, doi = {10.1088/2053-1583/aa62e8}, issn = {2053-1583}, year = {2017}, date = {2017-03-01}, journal = {2D Materials}, volume = {4}, number = {2}, pages = {022002}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Guterding, Daniel; Jeschke, Harald O; Mazin, I I; Glasbrenner, J K; Bascones, E; Valentí, Roser Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors Journal Article Physical Review Letters, 118 (1), pp. 017204, 2017, ISSN: 0031-9007. @article{Guterding2017_PRL_Nontrivial, title = {Nontrivial Role of Interlayer Cation States in Iron-Based Superconductors}, author = {Daniel Guterding and Harald O Jeschke and I I Mazin and J K Glasbrenner and E Bascones and Roser Valent\'{i}}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.118.017204}, doi = {10.1103/PhysRevLett.118.017204}, issn = {0031-9007}, year = {2017}, date = {2017-01-01}, journal = {Physical Review Letters}, volume = {118}, number = {1}, pages = {017204}, publisher = {American Physical Society}, keywords = {}, pubstate = {published}, tppubtype = {article} } |
Oliver, Sean M; Beams, Ryan; Krylyuk, Sergiy; Kalish, Irina; Singh, Arunima K; Bruma, Alina; Tavazza, Francesca; Joshi, Jaydeep; Stone, Iris R; Stranick, Stephan J; Davydov, Albert V; Vora, Patrick M The structural phases and vibrational properties of Mo 1−x W x Te 2 alloys Journal Article 2D Materials, 4 (4), pp. 045008, 2017, ISSN: 2053-1583. @article{Oliver2017b, title = {The structural phases and vibrational properties of Mo 1−x W x Te 2 alloys}, author = {Sean M Oliver and Ryan Beams and Sergiy Krylyuk and Irina Kalish and Arunima K Singh and Alina Bruma and Francesca Tavazza and Jaydeep Joshi and Iris R Stone and Stephan J Stranick and Albert V Davydov and Patrick M Vora}, url = {http://arxiv.org/abs/1703.10985%0Ahttp://dx.doi.org/10.1088/2053-1583/aa7a32 http://stacks.iop.org/2053-1583/4/i=4/a=045008?key=crossref.6ba8b9b9212ad2239ec721d728eec57f}, doi = {10.1088/2053-1583/aa7a32}, issn = {2053-1583}, year = {2017}, date = {2017-08-01}, journal = {2D Materials}, volume = {4}, number = {4}, pages = {045008}, publisher = {IOP Publishing}, abstract = {The structural polymorphism in transition metal dichalcogenides (TMDs) provides exciting opportunities for developing advanced electronics. For example, MoTe$_2$ crystallizes in the 2H semiconducting phase at ambient temperature and pressure, but transitions into the 1T$^backslashprime$ semimetallic phase at high temperatures. Alloying MoTe$_2$ with WTe$_2$ reduces the energy barrier between these two phases, while also allowing access to the T$_d$ Weyl semimetal phase. The MoWTe$_2$ alloy system is therefore promising for developing phase change memory technology. However, achieving this goal necessitates a detailed understanding of the phase composition in the MoTe$_2$-WTe$_2$ system. We combine polarization-resolved Raman spectroscopy with X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) to study MoWTe$_2$ alloys over the full compositional range x from 0 to 1. We identify Raman and XRD signatures characteristic of the 2H, 1T$^backslashprime$, and T$_d$ structural phases that agree with density-functional theory (DFT) calculations, and use them to identify phase fields in the MoTe$_2$-WTe$_2$ system, including single-phase 2H, 1T$^backslashprime$, and T$_d$ regions, as well as a two-phase 1T$^backslashprime$ + T$_d$ region. Disorder arising from compositional fluctuations in MoWTe$_2$ alloys breaks inversion and translational symmetry, leading to the activation of an infrared 1T$^backslashprime$-MoTe$_2$ mode and the enhancement of a double-resonance Raman process in 2H-MoWTe$_2$ alloys. Compositional fluctuations limit the phonon correlation length, which we estimate by fitting the observed asymmetric Raman lineshapes with a phonon confinement model. These observations reveal the important role of disorder in MoWTe$_2$ alloys, clarify the structural phase boundaries, and provide a foundation for future explorations of phase transitions and electronic phenomena in this system.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The structural polymorphism in transition metal dichalcogenides (TMDs) provides exciting opportunities for developing advanced electronics. For example, MoTe$_2$ crystallizes in the 2H semiconducting phase at ambient temperature and pressure, but transitions into the 1T$^backslashprime$ semimetallic phase at high temperatures. Alloying MoTe$_2$ with WTe$_2$ reduces the energy barrier between these two phases, while also allowing access to the T$_d$ Weyl semimetal phase. The MoWTe$_2$ alloy system is therefore promising for developing phase change memory technology. However, achieving this goal necessitates a detailed understanding of the phase composition in the MoTe$_2$-WTe$_2$ system. We combine polarization-resolved Raman spectroscopy with X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) to study MoWTe$_2$ alloys over the full compositional range x from 0 to 1. We identify Raman and XRD signatures characteristic of the 2H, 1T$^backslashprime$, and T$_d$ structural phases that agree with density-functional theory (DFT) calculations, and use them to identify phase fields in the MoTe$_2$-WTe$_2$ system, including single-phase 2H, 1T$^backslashprime$, and T$_d$ regions, as well as a two-phase 1T$^backslashprime$ + T$_d$ region. Disorder arising from compositional fluctuations in MoWTe$_2$ alloys breaks inversion and translational symmetry, leading to the activation of an infrared 1T$^backslashprime$-MoTe$_2$ mode and the enhancement of a double-resonance Raman process in 2H-MoWTe$_2$ alloys. Compositional fluctuations limit the phonon correlation length, which we estimate by fitting the observed asymmetric Raman lineshapes with a phonon confinement model. These observations reveal the important role of disorder in MoWTe$_2$ alloys, clarify the structural phase boundaries, and provide a foundation for future explorations of phase transitions and electronic phenomena in this system. |