1
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Zhu S, Duan R, Xu X, Sun F, Chen W, Wang F, Li S, Ye M, Zhou X, Cheng J, Wu Y, Liang H, Kono J, Li X, Liu Z, Wang QJ. Strong nonlinear optical processes with extraordinary polarization anisotropy in inversion-symmetry broken two-dimensional PdPSe. LIGHT, SCIENCE & APPLICATIONS 2024; 13:119. [PMID: 38802363 PMCID: PMC11130276 DOI: 10.1038/s41377-024-01474-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Revised: 05/03/2024] [Accepted: 05/09/2024] [Indexed: 05/29/2024]
Abstract
Nonlinear optical activities, especially second harmonic generation (SHG), are key phenomena in inversion-symmetry-broken two-dimensional (2D) transition metal dichalcogenides (TMDCs). On the other hand, anisotropic nonlinear optical processes are important for unique applications in nano-nonlinear photonic devices with polarization functions, having become one of focused research topics in the field of nonlinear photonics. However, the strong nonlinearity and strong optical anisotropy do not exist simultaneously in common 2D materials. Here, we demonstrate strong second-order and third-order susceptibilities of 64 pm/V and 6.2×10-19 m2/V2, respectively, in the even-layer PdPSe, which has not been discovered in other common TMDCs (e.g., MoS2). Strikingly, it also simultaneously exhibited strong SHG anisotropy with an anisotropic ratio of ~45, which is the largest reported among all 2D materials to date, to the best of our knowledge. In addition, the SHG anisotropy ratio can be harnessed from 0.12 to 45 (375 times) by varying the excitation wavelength due to the dispersion ofχ ( 2 ) values. As an illustrative example, we further demonstrate polarized SHG imaging for potential applications in crystal orientation identification and polarization-dependent spatial encoding. These findings in 2D PdPSe are promising for nonlinear nanophotonic and optoelectronic applications.
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Affiliation(s)
- Song Zhu
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Ruihuan Duan
- School of Material Science and Engineering, Nanyang Technological University, 639798, Singapore, Singapore
- CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Nanyang Technological University, 637371, Singapore, Singapore
| | - Xiaodong Xu
- School of Materials Science and Engineering, Harbin Institute of Technology, 150001, Harbin, China
| | - Fangyuan Sun
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Wenduo Chen
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Fakun Wang
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Siyuan Li
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Ming Ye
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Xin Zhou
- Department of Chemistry, National University of Singapore, 117543, Singapore, Singapore
| | - Jinluo Cheng
- GPL Photonics Lab, State Key Laboratory of Applied Optics, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, 130033, Changchun, China
| | - Yao Wu
- School of Material Science and Engineering, Nanyang Technological University, 639798, Singapore, Singapore
| | - Houkun Liang
- School of Electronics and Information Engineering, Sichuan University, 610064, Chengdu, Sichuan, China
| | - Junichiro Kono
- School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore, Singapore
- Departments of Electrical and Computer Engineering, Physics and Astronomy, and Materials Science and NanoEngineering, Rice University, Houston, TX, USA
| | - Xingji Li
- School of Materials Science and Engineering, Harbin Institute of Technology, 150001, Harbin, China.
| | - Zheng Liu
- School of Material Science and Engineering, Nanyang Technological University, 639798, Singapore, Singapore.
- CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Nanyang Technological University, 637371, Singapore, Singapore.
| | - Qi Jie Wang
- School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore, Singapore.
- CINTRA CNRS/NTU/THALES, UMI 3288, Research Techno Plaza, Nanyang Technological University, 637371, Singapore, Singapore.
- School of Physical and Mathematical Sciences, Nanyang Technological University, 637371, Singapore, Singapore.
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2
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Zhang Y, Gao B, Lepage D, Tong Y, Wang P, Xia W, Niu J, Feng Y, Chen H, Qian H. Large second-order susceptibility from a quantized indium tin oxide monolayer. NATURE NANOTECHNOLOGY 2024; 19:463-470. [PMID: 38168927 DOI: 10.1038/s41565-023-01574-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 11/13/2023] [Indexed: 01/05/2024]
Abstract
Due to their high optical transparency and electrical conductivity, indium tin oxide thin films are a promising material for photonic circuit design and applications. However, their weak optical nonlinearity has been a substantial barrier to nonlinear signal processing applications. In this study, we show that an atomically thin (~1.5 nm) indium tin oxide film in the form of an air/indium tin oxide/SiO2 quantum well exhibits a second-order susceptibility χ2 of ~1,800 pm V-1. First-principles calculations and quantum electrostatic modelling point to an electronic interband transition resonance in the asymmetric potential energy of the quantum well as the reason for this large χ2 value. As the χ2 value is more than 20 times higher than that of the traditional nonlinear LiNbO3 crystal, our indium tin oxide quantum well design can be an important step towards nonlinear photonic circuit applications.
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Affiliation(s)
- Yiyun Zhang
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China
| | - Bingtao Gao
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China
| | - Dominic Lepage
- Institut Quantique, Université de Sherbrooke, Sherbrooke, Quebec, Canada
| | - Yuanbiao Tong
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, China
| | - Pan Wang
- State Key Laboratory of Modern Optical Instrumentation, College of Optical Science and Engineering, Zhejiang University, Hangzhou, China
| | - Wendi Xia
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China
| | - Junru Niu
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China
| | - Yiming Feng
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China
| | - Hongsheng Chen
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China.
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China.
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China.
| | - Haoliang Qian
- Interdisciplinary Center for Quantum Information, State Key Laboratory of Extreme Photonics and Instrumentation, ZJU-Hangzhou Global Scientific and Technological Innovation Center, Zhejiang University, Hangzhou, China.
- International Joint Innovation Center, Key Laboratory of Advanced Micro/Nano Electronic Devices and Smart Systems of Zhejiang, Electromagnetics Academy at Zhejiang University, Zhejiang University, Haining, China.
- Jinhua Institute of Zhejiang University, Zhejiang University, Jinhua, China.
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3
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Yang H, Hu R, Wu H, He X, Zhou Y, Xue Y, He K, Hu W, Chen H, Gong M, Zhang X, Tan PH, Hernández ER, Xie Y. Identification and Structural Characterization of Twisted Atomically Thin Bilayer Materials by Deep Learning. NANO LETTERS 2024; 24:2789-2797. [PMID: 38407030 PMCID: PMC10921996 DOI: 10.1021/acs.nanolett.3c04815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 02/19/2024] [Accepted: 02/20/2024] [Indexed: 02/27/2024]
Abstract
Two-dimensional materials are expected to play an important role in next-generation electronics and optoelectronic devices. Recently, twisted bilayer graphene and transition metal dichalcogenides have attracted significant attention due to their unique physical properties and potential applications. In this study, we describe the use of optical microscopy to collect the color space of chemical vapor deposition (CVD) of molybdenum disulfide (MoS2) and the application of a semantic segmentation convolutional neural network (CNN) to accurately and rapidly identify thicknesses of MoS2 flakes. A second CNN model is trained to provide precise predictions on the twist angle of CVD-grown bilayer flakes. This model harnessed a data set comprising over 10,000 synthetic images, encompassing geometries spanning from hexagonal to triangular shapes. Subsequent validation of the deep learning predictions on twist angles was executed through the second harmonic generation and Raman spectroscopy. Our results introduce a scalable methodology for automated inspection of twisted atomically thin CVD-grown bilayers.
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Affiliation(s)
- Haitao Yang
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Ruiqi Hu
- Department
of Materials Science and Engineering, University
of Delaware, Newark, Delaware 19716, United States
| | - Heng Wu
- State
Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Xiaolong He
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Yan Zhou
- State
Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Phonon
Engineering Research Center of Jiangsu Province, School of Physics
and Technology, Nanjing Normal University, Nanjing 210023, China
| | - Yizhe Xue
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Kexin He
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Wenshuai Hu
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Haosen Chen
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
| | - Mingming Gong
- School
of Materials Science and Engineering, Northwestern
Polytechnical University, Xi’an 710072, China
| | - Xin Zhang
- State
Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | - Ping-Heng Tan
- State
Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
| | | | - Yong Xie
- Key
Laboratory of Wide Band-Gap Semiconductor Technology & Shaanxi
Key Laboratory of High-Orbits-Electron Materials and Protection Technology
for Aerospace, School of Advanced Materials and Nanotechnology, Xidian University, Xi’an 710071, China
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4
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Sun X, Suriyage M, Khan AR, Gao M, Zhao J, Liu B, Hasan MM, Rahman S, Chen RS, Lam PK, Lu Y. Twisted van der Waals Quantum Materials: Fundamentals, Tunability, and Applications. Chem Rev 2024; 124:1992-2079. [PMID: 38335114 DOI: 10.1021/acs.chemrev.3c00627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2024]
Abstract
Twisted van der Waals (vdW) quantum materials have emerged as a rapidly developing field of two-dimensional (2D) semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single photon emission, nonlinear optical response, magnon physics, and topological superconductivity. These captivating electronic and optical properties result from, and can be tailored by, the interlayer coupling using moiré patterns formed by vertically stacking atomic layers with controlled angle misorientation or lattice mismatch. Their outstanding properties and the high degree of tunability position them as compelling building blocks for both compact quantum-enabled devices and classical optoelectronics. This paper offers a comprehensive review of recent advancements in the understanding and manipulation of twisted van der Waals structures and presents a survey of the state-of-the-art research on moiré superlattices, encompassing interdisciplinary interests. It delves into fundamental theories, synthesis and fabrication, and visualization techniques, and the wide range of novel physical phenomena exhibited by these structures, with a focus on their potential for practical device integration in applications ranging from quantum information to biosensors, and including classical optoelectronics such as modulators, light emitting diodes, lasers, and photodetectors. It highlights the unique ability of moiré superlattices to connect multiple disciplines, covering chemistry, electronics, optics, photonics, magnetism, topological and quantum physics. This comprehensive review provides a valuable resource for researchers interested in moiré superlattices, shedding light on their fundamental characteristics and their potential for transformative applications in various fields.
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Affiliation(s)
- Xueqian Sun
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Manuka Suriyage
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Ahmed Raza Khan
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Department of Industrial and Manufacturing Engineering, University of Engineering and Technology (Rachna College Campus), Gujranwala, Lahore 54700, Pakistan
| | - Mingyuan Gao
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- College of Engineering and Technology, Southwest University, Chongqing 400716, China
| | - Jie Zhao
- Department of Quantum Science & Technology, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Boqing Liu
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Md Mehedi Hasan
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Sharidya Rahman
- Department of Materials Science and Engineering, Monash University, Clayton, Victoria 3800, Australia
- ARC Centre of Excellence in Exciton Science, Monash University, Clayton, Victoria 3800, Australia
| | - Ruo-Si Chen
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Ping Koy Lam
- Department of Quantum Science & Technology, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Yuerui Lu
- School of Engineering, College of Engineering and Computer Science, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
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5
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Lin KQ, Faria Junior PE, Hübner R, Ziegler JD, Bauer JM, Buchner F, Florian M, Hofmann F, Watanabe K, Taniguchi T, Fabian J, Steinhoff A, Chernikov A, Bange S, Lupton JM. Ultraviolet interlayer excitons in bilayer WSe 2. NATURE NANOTECHNOLOGY 2024; 19:196-201. [PMID: 38049597 DOI: 10.1038/s41565-023-01544-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Accepted: 10/15/2023] [Indexed: 12/06/2023]
Abstract
Interlayer excitons in van der Waals heterostructures are fascinating for applications like exciton condensation, excitonic devices and moiré-induced quantum emitters. The study of these charge-transfer states has almost exclusively focused on band edges, limiting the spectral region to the near-infrared regime. Here we explore the above-gap analogues of interlayer excitons in bilayer WSe2 and identify both neutral and charged species emitting in the ultraviolet. Even though the transitions occur far above the band edge, the states remain metastable, exhibiting linewidths as narrow as 1.8 meV. These interlayer high-lying excitations have switchable dipole orientations and hence show prominent Stark splitting. The positive and negative interlayer high-lying trions exhibit significant binding energies of 20-30 meV, allowing for a broad tunability of transitions via electric fields and electrostatic doping. The Stark splitting of these trions serves as a highly accurate, built-in sensor for measuring interlayer electric field strengths, which are exceedingly difficult to quantify otherwise. Such excitonic complexes are further sensitive to the interlayer twist angle and offer opportunities to explore emergent moiré physics under electrical control. Our findings more than double the accessible energy range for applications based on interlayer excitons.
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Affiliation(s)
- Kai-Qiang Lin
- State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China.
- Department of Physics, University of Regensburg, Regensburg, Germany.
| | | | - Ruven Hübner
- Institute for Theoretical Physics and Bremen Center for Computational Materials Science, University of Bremen, Bremen, Germany
| | - Jonas D Ziegler
- Institute of Applied Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, Dresden, Germany
| | - Jonas M Bauer
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Fabian Buchner
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Matthias Florian
- Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI, USA
| | - Felix Hofmann
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Kenji Watanabe
- Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Jaroslav Fabian
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Alexander Steinhoff
- Institute for Theoretical Physics and Bremen Center for Computational Materials Science, University of Bremen, Bremen, Germany
| | - Alexey Chernikov
- Institute of Applied Physics and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, Dresden, Germany
| | - Sebastian Bange
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - John M Lupton
- Department of Physics, University of Regensburg, Regensburg, Germany
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6
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Wu B, Zheng H, Li S, Wang CT, Ding J, He J, Liu Z, Wang JT, Liu Y. Enhanced Homogeneity of Moiré Superlattices in Double-Bilayer WSe 2 Homostructure. ACS APPLIED MATERIALS & INTERFACES 2023; 15:48475-48484. [PMID: 37796741 DOI: 10.1021/acsami.3c06949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/07/2023]
Abstract
Moiré superlattices have emerged as a promising platform for investigating and designing optically generated excitonic properties. The electronic band structure of these systems can be qualitatively modulated by interactions between the top and bottom layers, leading to the emergence of new quantum phenomena. However, the inhomogeneities present in atomically thin bilayer moiré superlattices created by artificial stacking have hindered a deeper understanding of strongly correlated electron properties. In this work, we report the fabrication of homogeneous moiré superlattices with controllable twist angles using a 2L-WSe2/2L-WSe2 homostructure. By adding extra layers, we provide additional degrees of freedom to tune the optical properties of the moiré superlattices while mitigating the nonuniformity problem. The presence of an additional bottom layer acts as a buffer, reducing the inhomogeneity of the moiré superlattice, while the encapsulation effect of the additional top and bottom WSe2 monolayers further enhances the localized moiré excitons. Our observations of alternating circularly polarized photoluminescence confirm the existence of moiré excitons, and their characteristics were further confirmed by theoretical calculations. These findings provide a fundamental basis for studying moiré potential correlated quantum phenomena and pave the way for their application in quantum optical devices.
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Affiliation(s)
- Biao Wu
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
- State Key Laboratory of High-Performance Complex Manufacturing, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
| | - Haihong Zheng
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
- State Key Laboratory of High-Performance Complex Manufacturing, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
| | - Shaofei Li
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
| | - Chang-Tian Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
| | - Junnan Ding
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
| | - Jun He
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
| | - Zongwen Liu
- School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, NSW 2006, Australia
- The University of Sydney Nano Institute, The University of Sydney, Sydney, NSW 2006 ,Australia
| | - Jian-Tao Wang
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
- School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, People's Republic of China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, People's Republic of China
| | - Yanping Liu
- School of Physics and Electronics, Hunan Key Laboratory for Super-microstructure and Ultrafast Process, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
- State Key Laboratory of High-Performance Complex Manufacturing, Central South University, 932 South Lushan Road, Changsha, Hunan 410083, People's Republic of China
- Shenzhen Research Institute of Central South University, Shenzhen 518000, People's Republic of China
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7
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Yuan Y, Liu P, Wu H, Chen H, Zheng W, Peng G, Zhu Z, Zhu M, Dai J, Qin S, Novoselov KS. Probing the Twist-Controlled Interlayer Coupling in Artificially Stacked Transition Metal Dichalcogenide Bilayers by Second-Harmonic Generation. ACS NANO 2023; 17:17897-17907. [PMID: 37698446 DOI: 10.1021/acsnano.3c03795] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/13/2023]
Abstract
Interlayer coupling plays a critical role in the electronic band structures and optoelectronic properties of van der Waals (vdW) materials and heterostructures. Here, we utilize optical second-harmonic generation (SHG) measurements to probe the twist-controlled interlayer coupling in artificially stacked WSe2/WSe2 homobilayers and WSe2/WS2 and WSe2/MoS2 heterobilayers with a postannealing procedure. In the large angle twisted WSe2/WSe2 and WSe2/WS2, the angular dependence of the SHG intensity follows the interference relations up to angles above 10°. For lower angles, the SHG is significantly suppressed. Furthermore, for the twisted WSe2/MoS2 the SHG intensity largely deviates from the coherent superposition model and shows consistent quenching for all the stacking angles. The suppressed SHG in twisted transition metal dichalcogenide (TMDC) bilayers is predominantly attributed to the interlayer coupling between the two adjacent monolayers. The evolution of the interlayer Raman mode in WSe2 demonstrates that the interlayer coupling in the twisted WSe2/WSe2 and WSe2/WS2 is highly angle-dependent. Alternatively, the interlayer coupling generally exists in the twisted WSe2/MoS2, regardless of the different angles. The interlayer coupling is further confirmed by the quenching and red-shift of the photoluminescence of WSe2 in the twisted TMDC bilayers. Combined with density functional theory calculations, we reveal that the stacking-angle-modulated interlayer coupling originates from the variation of the interlayer spacing and the binding energy in the twisted TMDC bilayers.
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Affiliation(s)
- Yuanjian Yuan
- College of Science & Hunan Key Laboratory of Extreme Matter and Applications, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Peng Liu
- College of Science & Hunan Key Laboratory of Extreme Matter and Applications, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Hongjian Wu
- College of Science & Hunan Key Laboratory of Extreme Matter and Applications, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Haitao Chen
- College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
- Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Weihao Zheng
- College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
- Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Gang Peng
- College of Science & Hunan Key Laboratory of Extreme Matter and Applications, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Zhihong Zhu
- College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
- Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Mengjian Zhu
- College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
- Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Jiayu Dai
- College of Science & Hunan Key Laboratory of Extreme Matter and Applications, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Shiqiao Qin
- College of Advanced Interdisciplinary Studies & Hunan Provincial Key Laboratory of Novel Nano-optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha, Hunan 410073, China
- Nanhu Laser Laboratory, National University of Defense Technology, Changsha, Hunan 410073, China
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore 117544
- Department of Materials Science and Engineering, National University of Singapore, Singapore 117575
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8
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Zhao S, Li Z, Huang X, Rupp A, Göser J, Vovk IA, Kruchinin SY, Watanabe K, Taniguchi T, Bilgin I, Baimuratov AS, Högele A. Excitons in mesoscopically reconstructed moiré heterostructures. NATURE NANOTECHNOLOGY 2023; 18:572-579. [PMID: 36973398 DOI: 10.1038/s41565-023-01356-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2022] [Accepted: 02/21/2023] [Indexed: 06/18/2023]
Abstract
Moiré effects in vertical stacks of two-dimensional crystals give rise to new quantum materials with rich transport and optical phenomena that originate from modulations of atomic registries within moiré supercells. Due to finite elasticity, however, the superlattices can transform from moiré-type to periodically reconstructed patterns. Here we expand the notion of such nanoscale lattice reconstruction to the mesoscopic scale of laterally extended samples and demonstrate rich consequences in optical studies of excitons in MoSe2-WSe2 heterostructures with parallel and antiparallel alignments. Our results provide a unified perspective on moiré excitons in near-commensurate semiconductor heterostructures with small twist angles by identifying domains with exciton properties of distinct effective dimensionality, and establish mesoscopic reconstruction as a compelling feature of real samples and devices with inherent finite size effects and disorder. Generalized to stacks of other two-dimensional materials, this notion of mesoscale domain formation with emergent topological defects and percolation networks will instructively expand the understanding of fundamental electronic, optical and magnetic properties of van der Waals heterostructures.
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Affiliation(s)
- Shen Zhao
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany.
| | - Zhijie Li
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany
| | - Xin Huang
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany
- Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, P. R. China
- School of Physical Sciences, CAS Key Laboratory of Vacuum Physics, University of Chinese Academy of Sciences, Beijing, P. R. China
| | - Anna Rupp
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany
| | - Jonas Göser
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany
| | - Ilia A Vovk
- PhysNano Department, ITMO University, Saint Petersburg, Russia
| | - Stanislav Yu Kruchinin
- Center for Computational Materials Sciences, Faculty of Physics, University of Vienna, Vienna, Austria
- Nuance Communications Austria GmbH, Vienna, Austria
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Ismail Bilgin
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany
| | - Anvar S Baimuratov
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany.
| | - Alexander Högele
- Fakultät für Physik, Munich Quantum Center, and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Munich, Germany.
- Munich Center for Quantum Science and Technology (MCQST), München, Germany.
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9
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Woźniak T, Faria Junior PE, Ramzan MS, Kuc AB. Electronic and Excitonic Properties of MSi 2 Z 4 Monolayers. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2206444. [PMID: 36772899 DOI: 10.1002/smll.202206444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Revised: 01/20/2023] [Indexed: 05/11/2023]
Abstract
MA2 Z4 monolayers form a new class of hexagonal non-centrosymmetric materials hosting extraordinary spin-valley physics. While only two compounds (MoSi2 N4 and WSi2 N4 ) are recently synthesized, theory predicts interesting (opto)electronic properties of a whole new family of such two-dimensional (2D) materials. Here, the chemical trends of band gaps and spin-orbit splittings of bands in selected MSi2 Z4 (M = Mo, W; Z = N, P, As, Sb) compounds are studied from first-principles. Effective Bethe-Salpeter-equation-based calculations reveal high exciton binding energies. Evolution of excitonic energies under external magnetic field is predicted by providing their effective g-factors and diamagnetic coefficients, which can be directly compared to experimental values. In particular, large positive g-factors are predicted for excitons involving higher conduction bands. In view of these predictions, MSi2 Z4 monolayers yield a new platform to study excitons and are attractive for optoelectronic devices, also in the form of heterostructures. In addition, a spin-orbit induced bands inversion is observed in the heaviest studied compound, WSi2 Sb4 , a hallmark of its topological nature.
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Affiliation(s)
- Tomasz Woźniak
- Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wrocław, 50-370, Poland
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
- Helmholtz-Zentrum Dresden-Rossendorf, Abteilung Ressourcenökologie, Forschungsstelle Leipzig, Permoserstr. 15, 04318, Leipzig, Germany
| | - Paulo E Faria Junior
- Institute for Theoretical Physics, University of Regensburg, Universitätsstraße 31, 93040, Regensburg, Germany
| | - Muhammad S Ramzan
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
- Helmholtz-Zentrum Dresden-Rossendorf, Abteilung Ressourcenökologie, Forschungsstelle Leipzig, Permoserstr. 15, 04318, Leipzig, Germany
- Institut für Physik, Carl von Ossietzky Universität Oldenburg, 26129, Oldenburg, Germany
| | - Agnieszka B Kuc
- Department of Physics and Earth Sciences, Jacobs University Bremen, Campus Ring 1, 28759, Bremen, Germany
- Helmholtz-Zentrum Dresden-Rossendorf, Abteilung Ressourcenökologie, Forschungsstelle Leipzig, Permoserstr. 15, 04318, Leipzig, Germany
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10
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Faria Junior PE, Fabian J. Signatures of Electric Field and Layer Separation Effects on the Spin-Valley Physics of MoSe 2/WSe 2 Heterobilayers: From Energy Bands to Dipolar Excitons. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:1187. [PMID: 37049281 PMCID: PMC10096971 DOI: 10.3390/nano13071187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2023] [Revised: 03/22/2023] [Accepted: 03/24/2023] [Indexed: 06/19/2023]
Abstract
Multilayered van der Waals heterostructures based on transition metal dichalcogenides are suitable platforms on which to study interlayer (dipolar) excitons, in which electrons and holes are localized in different layers. Interestingly, these excitonic complexes exhibit pronounced valley Zeeman signatures, but how their spin-valley physics can be further altered due to external parameters-such as electric field and interlayer separation-remains largely unexplored. Here, we perform a systematic analysis of the spin-valley physics in MoSe2/WSe2 heterobilayers under the influence of an external electric field and changes of the interlayer separation. In particular, we analyze the spin (Sz) and orbital (Lz) degrees of freedom, and the symmetry properties of the relevant band edges (at K, Q, and Γ points) of high-symmetry stackings at 0° (R-type) and 60° (H-type) angles-the important building blocks present in moiré or atomically reconstructed structures. We reveal distinct hybridization signatures on the spin and the orbital degrees of freedom of low-energy bands, due to the wave function mixing between the layers, which are stacking-dependent, and can be further modified by electric field and interlayer distance variation. We find that H-type stackings favor large changes in the g-factors as a function of the electric field, e.g., from -5 to 3 in the valence bands of the Hhh stacking, because of the opposite orientation of Sz and Lz of the individual monolayers. For the low-energy dipolar excitons (direct and indirect in k-space), we quantify the electric dipole moments and polarizabilities, reflecting the layer delocalization of the constituent bands. Furthermore, our results show that direct dipolar excitons carry a robust valley Zeeman effect nearly independent of the electric field, but tunable by the interlayer distance, which can be rendered experimentally accessible via applied external pressure. For the momentum-indirect dipolar excitons, our symmetry analysis indicates that phonon-mediated optical processes can easily take place. In particular, for the indirect excitons with conduction bands at the Q point for H-type stackings, we find marked variations of the valley Zeeman (∼4) as a function of the electric field, which notably stands out from the other dipolar exciton species. Our analysis suggests that stronger signatures of the coupled spin-valley physics are favored in H-type stackings, which can be experimentally investigated in samples with twist angle close to 60°. In summary, our study provides fundamental microscopic insights into the spin-valley physics of van der Waals heterostructures, which are relevant to understanding the valley Zeeman splitting of dipolar excitonic complexes, and also intralayer excitons.
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11
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Wu Q, Liang F, Kang L, Wu J, Lin Z. Sliding Modulation in Nonlinear Optical Effect in Two-Dimensional van der Waals Cu 2MoS 4. ACS APPLIED MATERIALS & INTERFACES 2022; 14:9535-9543. [PMID: 35148072 DOI: 10.1021/acsami.1c24696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Owing to different nonlinear optical (NLO) motifs with diverse structural and symmetrical assemblies, two-dimensional (2D) van der Waals (vdW) transition metal ternary chalcogenides (TMTCs) have unique advantages in nano-NLO modulation compared to 2D vdW transition metal dichalcogenides (e.g., MoS2). Based on first-principles calculations, in this study, we discover that layered Cu2MoS4 with two tetrahedral [MoS4] and [CuS4] motifs, as a representative 2D vdW TMTC, has an extremely rare sliding-modulated second harmonic effect with nearly 70% fluctuation, much larger than 5% in MoS2 with a single octahedral [MoS6] motif because of different synergistic effects among intra- and interlayer NLO polarizations induced by the [CuS4] and [MoS4] NLO-active motifs. Furthermore, the Cu2MoS4 layers exhibit a low energy barrier in interlayer sliding with a robust SHG response against large strains, displaying a novel and applicable NLO-modulation mechanism in nano-optoelectronics.
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Affiliation(s)
- Qingchen Wu
- Functional Crystals Lab, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Fei Liang
- Functional Crystals Lab, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Lei Kang
- Functional Crystals Lab, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
| | - Jian Wu
- Department of Physics, Tsinghua University, Beijing 100084, China
| | - Zheshuai Lin
- Functional Crystals Lab, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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12
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Zheng G, Wang T, Lou Q, Shen C, Wu M, Sun J, Ji W, Zang J, Liu K, Dong L, Shan C. Localized Excitonic Electroluminescence from Carbon Nanodots. J Phys Chem Lett 2022; 13:1587-1595. [PMID: 35139310 DOI: 10.1021/acs.jpclett.1c04028] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Localized excitons are expected to achieve high-performance electroluminescence and have been widely investigated in GaN-based light-emitting diodes (LEDs). Although carbon nanodot (CD) based LEDs have been achieved with the radiative recombination of electrons and holes, localized excitonic electroluminescence has been not reported before. In this Letter, localized excitonic electroluminescent devices have been fabricated using fluorescent CDs as an active layer. The CDs show strong localized excitonic yellow emission with a fluorescence quantum yield of 76% and Stokes shift of 2.1 eV. The CD-based LEDs present a sub-bandgap turn-on voltage of 2.4 V and a maximum luminance of 60.2 cd m-2, which is the lowest driving voltage among the CD-based electroluminescent devices. Localized centers trap carriers effectively, resulting in sub-bandgap light emission. The current results manifest that localized excitons may furnish a promising approach to boost the development of CD-based LEDs.
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Affiliation(s)
- Guangsong Zheng
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Ting Wang
- Key Lab of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130023, China
| | - Qing Lou
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Chenglong Shen
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Mengyuan Wu
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Junlu Sun
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Wenyu Ji
- Key Lab of Physics and Technology for Advanced Batteries (Ministry of Education), College of Physics, Jilin University, Changchun 130023, China
| | - Jinhao Zang
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Kaikai Liu
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Lin Dong
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
| | - Chongxin Shan
- Henan Key Laboratory of Diamond Optoelectronic Materials and Devices, Key Laboratory of Material Physics, Ministry of Education, School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
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13
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Lin KQ, Ong CS, Bange S, Faria Junior PE, Peng B, Ziegler JD, Zipfel J, Bäuml C, Paradiso N, Watanabe K, Taniguchi T, Strunk C, Monserrat B, Fabian J, Chernikov A, Qiu DY, Louie SG, Lupton JM. Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe 2. Nat Commun 2021; 12:5500. [PMID: 34535654 PMCID: PMC8448890 DOI: 10.1038/s41467-021-25499-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 07/28/2021] [Indexed: 11/23/2022] Open
Abstract
Monolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe2 with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons. Here, the authors report on evidence of an excitonic species formed by electrons in high-energy conduction band states with a negative effective mass, explaining previous observations of quantum interference phenomena in two-dimensional semiconductors.
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Affiliation(s)
- Kai-Qiang Lin
- Department of Physics, University of Regensburg, Regensburg, Germany.
| | - Chin Shen Ong
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - Sebastian Bange
- Department of Physics, University of Regensburg, Regensburg, Germany
| | | | - Bo Peng
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Jonas D Ziegler
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Jonas Zipfel
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Christian Bäuml
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Nicola Paradiso
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
| | - Christoph Strunk
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Bartomeu Monserrat
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.,Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
| | - Jaroslav Fabian
- Department of Physics, University of Regensburg, Regensburg, Germany
| | - Alexey Chernikov
- Department of Physics, University of Regensburg, Regensburg, Germany.,Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Würzburg-Dresden Cluster of Excellence ct.qmat, Technische Universität Dresden, Dresden, Germany
| | - Diana Y Qiu
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.,Department of Mechanical Engineering and Materials Science, Yale University, Yale, CT, USA
| | - Steven G Louie
- Department of Physics, University of California at Berkeley, Berkeley, CA, USA.,Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
| | - John M Lupton
- Department of Physics, University of Regensburg, Regensburg, Germany.
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