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Xie HY, Ghaemi P, Mitrano M, Uchoa B. Theory of topological exciton insulators and condensates in flat Chern bands. Proc Natl Acad Sci U S A 2024; 121:e2401644121. [PMID: 39178234 DOI: 10.1073/pnas.2401644121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 07/08/2024] [Indexed: 08/25/2024] Open
Abstract
Excitons are the neutral quasiparticles that form when Coulomb interactions create bound states between electrons and holes. Due to their bosonic nature, excitons are expected to condense and exhibit superfluidity at sufficiently low temperatures. In interacting Chern insulators, excitons may inherit the nontrivial topology and quantum geometry from the underlying electron wavefunctions. We theoretically investigate the excitonic bound states and superfluidity in flat-band insulators pumped with light. We find that the exciton wavefunctions exhibit vortex structures in momentum space, with the total vorticity being equal to the difference of Chern numbers between the conduction and valence bands. Moreover, both the exciton binding energy and the exciton superfluid density are proportional to the Brillouin-zone average of the quantum metric and the Coulomb potential energy per unit cell. Spontaneous emission of circularly polarized light from radiative decay is a detectable signature of the exciton vorticity. We propose that the vorticity can also be experimentally measured via the nonlinear anomalous Hall effect, whereas the exciton superfluidity can be detected by voltage-drop quantization through a combination of quantum geometry and Aharonov-Casher effect. Topological excitons and their superfluid phase could be realized in flat bands of twisted Van der Waals heterostructures.
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Affiliation(s)
- Hong-Yi Xie
- Department of Physics and Astronomy, Center for Quantum Research and Technology, University of Oklahoma, Norman, OK 73069
| | - Pouyan Ghaemi
- Department of Physics, City University of New York, New York, NY 10031
| | - Matteo Mitrano
- Department of Physics, Harvard University, Cambridge, MA, 02138
| | - Bruno Uchoa
- Department of Physics and Astronomy, Center for Quantum Research and Technology, University of Oklahoma, Norman, OK 73069
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Wu W, Sun S, Tang CS, Wu J, Ma Y, Zhang L, Cai C, Zhong J, Milošević MV, Wee ATS, Yin X. Realization of a 2D Lieb Lattice in a Metal-Inorganic Framework with Partial Flat Bands and Topological Edge States. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2024:e2405615. [PMID: 39180271 DOI: 10.1002/adma.202405615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2024] [Revised: 08/05/2024] [Indexed: 08/26/2024]
Abstract
Flat bands and Dirac cones in materials are the source of the exotic electronic and topological properties. The Lieb lattice is expected to host these electronic structures, arising from quantum destructive interference. Nevertheless, the experimental realization of a 2D Lieb lattice remained challenging to date due to its intrinsic structural instability. After computationally designing a Platinum-Phosphorus (Pt-P) Lieb lattice, it has successfully overcome its structural instability and synthesized on a gold substrate via molecular beam epitaxy. Low-temperature scanning tunneling microscopy and spectroscopy verify the Lieb lattice's morphology and electronic flat bands. Furthermore, topological Dirac edge states stemming from pronounced spin-orbit coupling induced by heavy Pt atoms are predicted. These findings convincingly open perspectives for creating metal-inorganic framework-based atomic lattices, offering prospects for strongly correlated phases interplayed with topology.
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Affiliation(s)
- Wenjun Wu
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
| | - Shuo Sun
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
| | - Chi Sin Tang
- Singapore Synchrotron Light Source (SSLS), National University of Singapore, Singapore, 117603, Singapore
| | - Jing Wu
- Institute of Materials Research and Ring (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore, 138634, Singapore
| | - Yu Ma
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
| | - Lingfeng Zhang
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
| | - Chuanbing Cai
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
| | - Jianxin Zhong
- Center for Quantum Science and Technology, Department of Physics, Shanghai University, Shanghai, 200444, China
| | - Milorad V Milošević
- Department of Physics & NANOlab Center of Excellence, University of Antwerp, Groenenborgerlaan 171, Antwerp, B-2020, Belgium
| | - Andrew T S Wee
- Department of Physics, Faculty of Science, National University of Singapore, Singapore, 117542, Singapore
- Centre for Advanced 2D Materials and Graphene Research, National University of Singapore, Singapore, 117546, Singapore
| | - Xinmao Yin
- Department of Physics, Shanghai Key Laboratory of High Temperature Superconductors, Shanghai University, Shanghai, 200444, China
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Verma N, Guerci D, Queiroz R. Geometric Stiffness in Interlayer Exciton Condensates. PHYSICAL REVIEW LETTERS 2024; 132:236001. [PMID: 38905692 DOI: 10.1103/physrevlett.132.236001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 03/28/2024] [Accepted: 05/06/2024] [Indexed: 06/23/2024]
Abstract
Recent experiments have confirmed the presence of interlayer excitons in the ground state of transition metal dichalcogenide bilayers. The interlayer excitons are expected to show remarkable transport properties when they undergo Bose condensation. In this Letter, we demonstrate that quantum geometry of Bloch wave functions plays an important role in the phase stiffness of the interlayer exciton condensate. Notably, we identify a geometric contribution that amplifies the stiffness, leading to the formation of a robust condensate with an increased Berezinskii-Kosterlitz-Thouless temperature. Our results have direct implications for the ongoing experimental efforts on interlayer excitons in materials that have nontrivial quantum geometry. We provide estimates for the geometric contribution in transition metal dichalcogenide bilayers through a realistic continuum model with gated Coulomb interaction, and find that the substantially increased stiffness may allow an interlayer exciton condensate to be realized at amenable experimental conditions.
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Pham TA, Kang SH, Ozbek Y, Yoon M, Zhang P. Distance-Dependent Evolution of Electronic States in Kagome-Honeycomb Lateral Heterostructures in FeSn. ACS NANO 2024; 18:8768-8776. [PMID: 38488038 DOI: 10.1021/acsnano.3c11381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
In this work, we demonstrate the formation and electronic influence of lateral heterointerfaces in FeSn containing Kagome and honeycomb layers. Lateral heterostructures offer spatially resolved property control, enabling the integration of dissimilar materials and promoting phenomena not typically observed in vertical heterostructures. Using the molecular beam epitaxy technique, we achieve a controllable synthesis of lateral heterostructures in the Kagome metal FeSn. With scanning tunneling microscopy/spectroscopy in conjunction with first-principles calculations, we provide a comprehensive understanding of the bonding motif connecting the Fe3Sn-terminated Kagome and Sn2-terminated honeycomb surfaces. More importantly, we reveal a distance-dependent evolution of the electronic states in the vicinity of the heterointerfaces. This evolution is significantly influenced by the orbital character of the flat bands. Our findings suggest an approach to modulate the electronic properties of the Kagome lattice, which should be beneficial for the development of future quantum devices.
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Affiliation(s)
- Tuan Anh Pham
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Seoung-Hun Kang
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Yasemin Ozbek
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
| | - Mina Yoon
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States
| | - Pengpeng Zhang
- Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, United States
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Wang H, Zhong Y, Jiang W, Latini S, Xia S, Cui T, Li Z, Low T, Liu F. Strain-Tunable Hyperbolic Exciton Polaritons in Monolayer Black Arsenic with Two Exciton Resonances. NANO LETTERS 2024; 24:2057-2062. [PMID: 38285001 DOI: 10.1021/acs.nanolett.3c04730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2024]
Abstract
Hyperbolic polaritons have been attracting increasing interest for applications in optoelectronics, biosensing, and super-resolution imaging. Here, we report the in-plane hyperbolic exciton polaritons in monolayer black-arsenic (B-As), where hyperbolicity arises strikingly from two exciton resonant peaks. Remarkably, the presence of two resonances at different momenta makes overall hyperbolicity highly tunable by strain, as the two exciton peaks can be merged into the same frequency to double the strength of hyperbolicity as well as light absorption under a 1.5% biaxial strain. Moreover, the frequency of the merged hyperbolicity can be further tuned from 1.35 to 0.8 eV by an anisotropic biaxial strain. Furthermore, electromagnetic numerical simulation reveals a strain-induced hyperbolicity, as manifested in a topological transition of iso-frequency contour of exciton polaritons. The good tunability, large exciton binding energy, and strong light absorption exhibited in the hyperbolic monolayer B-As make it highly suitable for nanophotonics applications under ambient conditions.
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Affiliation(s)
- Hongwei Wang
- Institute of High Pressure Physics, School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Yuhan Zhong
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Modern Optical Instrumentation, ZJU-Hangzhou Global Science and Technology Innovation Center, Zhejiang University, Hangzhou 310027, China
| | - Wei Jiang
- Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Simone Latini
- Nanomade, Department of Physics, Technical University of Denmark, 2800 Kongens Lyngby, Denmark
| | - Shengxuan Xia
- Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education and Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, China
| | - Tian Cui
- Institute of High Pressure Physics, School of Physical Science and Technology, Ningbo University, Ningbo 315211, China
| | - Zhenglu Li
- Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089, United States
| | - Tony Low
- Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Feng Liu
- Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112, United States
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Jin KH, Jiang W, Sethi G, Liu F. Topological quantum devices: a review. NANOSCALE 2023; 15:12787-12817. [PMID: 37490310 DOI: 10.1039/d3nr01288c] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/26/2023]
Abstract
The introduction of the concept of topology into condensed matter physics has greatly deepened our fundamental understanding of transport properties of electrons as well as all other forms of quasi particles in solid materials. It has also fostered a paradigm shift from conventional electronic/optoelectronic devices to novel quantum devices based on topology-enabled quantum device functionalities that transfer energy and information with unprecedented precision, robustness, and efficiency. In this article, the recent research progress in topological quantum devices is reviewed. We first outline the topological spintronic devices underlined by the spin-momentum locking property of topology. We then highlight the topological electronic devices based on quantized electron and dissipationless spin conductivity protected by topology. Finally, we discuss quantum optoelectronic devices with topology-redefined photoexcitation and emission. The field of topological quantum devices is only in its infancy, we envision many significant advances in the near future.
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Affiliation(s)
- Kyung-Hwan Jin
- Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang 37673, Republic of Korea
| | - Wei Jiang
- School of Physics, Beijing Institute of Technology, Beijing 100081, China
| | - Gurjyot Sethi
- Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112, USA.
| | - Feng Liu
- Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112, USA.
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