1
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Geng H, Tang J, Wu Y, Yu Y, Guest JR, Zhang R. Imaging Valley Excitons in a 2D Semiconductor with Scanning Tunneling Microscope-Induced Luminescence. ACS NANO 2024; 18:8961-8970. [PMID: 38470346 DOI: 10.1021/acsnano.3c12555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/13/2024]
Abstract
Valley excitons dominate the optoelectronic response of transition-metal dichalcogenides and are drastically affected by structural and environmental inhomogeneities localized in these materials. Critical to understanding and controlling these nanoscale excitonic changes is the ability to correlate the imaging of excitonic states with crystalline structures on the atomic scale. Here, we apply scanning tunneling microscope-induced luminescence microscopy to image valley excitons in a semiconducting transition-metal dichalcogenide monolayer decoupled by a 10 nanometer-thick hexagonal-boron-nitride flake incorporated in a lateral homojunction on an Au electrode surface. This design enables the observation of chiral excitonic emission arising from neutral and charged valley excitons of the monolayer semiconductor at ambipolar voltages with a quantum efficiency up to ∼10-5 photon/electron. The measured light helicity demonstrates considerable circular polarization dependent on the sample voltage, reaching as much as 40%. The real-space luminescence imaging maps─at subnanometer resolution─of the valley excitons reveal striking spatial variations associated with localized inhomogeneities, including surface impurities and possibly nanoscale dielectric and/or potential disorders in the monolayer. Our study introduces a promising format for 2D materials to explore and tailor their optoelectronic processes at the atomic scale.
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Affiliation(s)
- Hairui Geng
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Optoelectronic Information Acquisition and Manipulation, Ministry of Education, School of Physics and Optoelectronics Engineering, Anhui University, Hefei Anhui 230601, China
| | - Jie Tang
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Optoelectronic Information Acquisition and Manipulation, Ministry of Education, School of Physics and Optoelectronics Engineering, Anhui University, Hefei Anhui 230601, China
| | - Yanwei Wu
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Optoelectronic Information Acquisition and Manipulation, Ministry of Education, School of Physics and Optoelectronics Engineering, Anhui University, Hefei Anhui 230601, China
| | - Yuanqin Yu
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Optoelectronic Information Acquisition and Manipulation, Ministry of Education, School of Physics and Optoelectronics Engineering, Anhui University, Hefei Anhui 230601, China
| | - Jeffrey R Guest
- Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Rui Zhang
- Information Materials and Intelligent Sensing Laboratory of Anhui Province, Key Laboratory of Optoelectronic Information Acquisition and Manipulation, Ministry of Education, School of Physics and Optoelectronics Engineering, Anhui University, Hefei Anhui 230601, China
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2
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Blundo E, Tuzi F, Cianci S, Cuccu M, Olkowska-Pucko K, Kipczak Ł, Contestabile G, Miriametro A, Felici M, Pettinari G, Taniguchi T, Watanabe K, Babiński A, Molas MR, Polimeni A. Localisation-to-delocalisation transition of moiré excitons in WSe 2/MoSe 2 heterostructures. Nat Commun 2024; 15:1057. [PMID: 38316753 PMCID: PMC10844653 DOI: 10.1038/s41467-024-44739-9] [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: 04/24/2023] [Accepted: 01/02/2024] [Indexed: 02/07/2024] Open
Abstract
Moiré excitons (MXs) are electron-hole pairs localised by the periodic (moiré) potential forming in two-dimensional heterostructures (HSs). MXs can be exploited, e.g., for creating nanoscale-ordered quantum emitters and achieving or probing strongly correlated electronic phases at relatively high temperatures. Here, we studied the exciton properties of WSe2/MoSe2 HSs from T = 6 K to room temperature using time-resolved and continuous-wave micro-photoluminescence also under a magnetic field. The exciton dynamics and emission lineshape evolution with temperature show clear signatures that MXs de-trap from the moiré potential and turn into free interlayer excitons (IXs) for temperatures above 100 K. The MX-to-IX transition is also apparent from the exciton magnetic moment reversing its sign when the moiré potential is not capable of localising excitons at elevated temperatures. Concomitantly, the exciton formation and decay times reduce drastically. Thus, our findings establish the conditions for a truly confined nature of the exciton states in a moiré superlattice with increasing temperature and photo-generated carrier density.
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Affiliation(s)
- Elena Blundo
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy.
| | - Federico Tuzi
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Salvatore Cianci
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Marzia Cuccu
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Katarzyna Olkowska-Pucko
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093, Warsaw, Poland
| | - Łucja Kipczak
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093, Warsaw, Poland
| | - Giorgio Contestabile
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Antonio Miriametro
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Marco Felici
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy
| | - Giorgio Pettinari
- Institute for Photonics and Nanotechnologies, National Research Council, 00133, Rome, Italy
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Adam Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093, Warsaw, Poland
| | - Maciej R Molas
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093, Warsaw, Poland
| | - Antonio Polimeni
- Physics Department, Sapienza University of Rome, Piazzale Aldo Moro 5, 00185, Rome, Italy.
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3
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Mueller NS, Arul R, Kang G, Saunders AP, Johnson AC, Sánchez-Iglesias A, Hu S, Jakob LA, Bar-David J, de Nijs B, Liz-Marzán LM, Liu F, Baumberg JJ. Photoluminescence upconversion in monolayer WSe 2 activated by plasmonic cavities through resonant excitation of dark excitons. Nat Commun 2023; 14:5726. [PMID: 37714855 PMCID: PMC10504321 DOI: 10.1038/s41467-023-41401-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2023] [Accepted: 09/04/2023] [Indexed: 09/17/2023] Open
Abstract
Anti-Stokes photoluminescence (PL) is light emission at a higher photon energy than the excitation, with applications in optical cooling, bioimaging, lasing, and quantum optics. Here, we show how plasmonic nano-cavities activate anti-Stokes PL in WSe2 monolayers through resonant excitation of a dark exciton at room temperature. The optical near-fields of the plasmonic cavities excite the out-of-plane transition dipole of the dark exciton, leading to light emission from the bright exciton at higher energy. Through statistical measurements on hundreds of plasmonic cavities, we show that coupling to the dark exciton leads to a near hundred-fold enhancement of the upconverted PL intensity. This is further corroborated by experiments in which the laser excitation wavelength is tuned across the dark exciton. We show that a precise nanoparticle geometry is key for a consistent enhancement, with decahedral nanoparticle shapes providing an efficient PL upconversion. Finally, we demonstrate a selective and reversible switching of the upconverted PL via electrochemical gating. Our work introduces the dark exciton as an excitation channel for anti-Stokes PL in WSe2 and paves the way for large-area substrates providing nanoscale optical cooling, anti-Stokes lasing, and radiative engineering of excitons.
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Affiliation(s)
- Niclas S Mueller
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK.
- Fritz Haber Institute of the Max Planck Society, 14195, Berlin, Germany.
| | - Rakesh Arul
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Gyeongwon Kang
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
- Department of Chemistry, Kangwon National University, Chuncheon, 24341, South Korea
| | - Ashley P Saunders
- Department of Chemistry, Stanford University, Stanford, CA, 94305, USA
| | - Amalya C Johnson
- Department of Materials Science and Engineering, Stanford University, Stanford, CA, 94305, USA
| | - Ana Sánchez-Iglesias
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Paseo de Miramón 194, Donostia-San Sebastián, 20014, Spain
- Centro de Física de Materiales, CSIC-UPV/EHU, Manuel Lardizabal Ibilbidea 5, Donostia-San Sebastián, 20018, Spain
| | - Shu Hu
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Lukas A Jakob
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Jonathan Bar-David
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Bart de Nijs
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK
| | - Luis M Liz-Marzán
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Paseo de Miramón 194, Donostia-San Sebastián, 20014, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, 48009, Spain
- Centro de Investigación Biomédica en Red, Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Donostia-San Sebastián, 20014, Spain
| | - Fang Liu
- Department of Chemistry, Stanford University, Stanford, CA, 94305, USA
| | - Jeremy J Baumberg
- NanoPhotonics Centre, Cavendish Laboratory, Department of Physics, University of Cambridge, Cambridge, CB3 0HE, UK.
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4
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Chand SB, Woods JM, Quan J, Mejia E, Taniguchi T, Watanabe K, Alù A, Grosso G. Interaction-driven transport of dark excitons in 2D semiconductors with phonon-mediated optical readout. Nat Commun 2023; 14:3712. [PMID: 37349290 DOI: 10.1038/s41467-023-39339-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 06/08/2023] [Indexed: 06/24/2023] Open
Abstract
The growing field of quantum information technology requires propagation of information over long distances with efficient readout mechanisms. Excitonic quantum fluids have emerged as a powerful platform for this task due to their straightforward electro-optical conversion. In two-dimensional transition metal dichalcogenides, the coupling between spin and valley provides exciting opportunities for harnessing, manipulating, and storing bits of information. However, the large inhomogeneity of single layers cannot be overcome by the properties of bright excitons, hindering spin-valley transport. Nonetheless, the rich band structure supports dark excitonic states with strong binding energy and longer lifetime, ideally suited for long-range transport. Here we show that dark excitons can diffuse over several micrometers and prove that this repulsion-driven propagation is robust across non-uniform samples. The long-range propagation of dark states with an optical readout mediated by chiral phonons provides a new concept of excitonic devices for applications in both classical and quantum information technology.
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Affiliation(s)
- Saroj B Chand
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
| | - John M Woods
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
| | - Jiamin Quan
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
| | - Enrique Mejia
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, 305-0044, Japan
| | - Andrea Alù
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA
- Department of Electrical Engineering, City College of the City University of New York, New York, NY, 10031, USA
- Physics Program, Graduate Center, City University of New York, New York, NY, 10016, USA
| | - Gabriele Grosso
- Photonics Initiative, Advanced Science Research Center, City University of New York, New York, NY, 10031, USA.
- Physics Program, Graduate Center, City University of New York, New York, NY, 10016, USA.
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5
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Karmakar A, Kazimierczuk T, Antoniazzi I, Raczyński M, Park S, Jang H, Taniguchi T, Watanabe K, Babiński A, Al-Mahboob A, Molas MR. Excitation-Dependent High-Lying Excitonic Exchange via Interlayer Energy Transfer from Lower- to- Higher Bandgap 2D Material. NANO LETTERS 2023. [PMID: 37289519 DOI: 10.1021/acs.nanolett.3c01127] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
High light absorption (∼15%) and strong photoluminescence (PL) emission in monolayer (1L) transition metal dichalcogenides (TMDs) make them ideal candidates for optoelectronic device applications. Competing interlayer charge transfer (CT) and energy transfer (ET) processes control the photocarrier relaxation pathways in TMD heterostructures (HSs). In TMDs, long-distance ET can survive up to several tens of nm, unlike the CT process. Our experiment shows that an efficient ET occurs from the 1Ls WSe2-to-MoS2 with an interlayer hexagonal boron nitride (hBN), due to the resonant overlapping of the high-lying excitonic states between the two TMDs, resulting in enhanced HS MoS2 PL emission. This type of unconventional ET from the lower-to-higher optical bandgap material is not typical in the TMD HSs. With increasing temperature, the ET process becomes weaker due to the increased electron-phonon scattering, destroying the enhanced MoS2 emission. Our work provides new insight into the long-distance ET process and its effect on the photocarrier relaxation pathways.
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Affiliation(s)
- Arka Karmakar
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Tomasz Kazimierczuk
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Igor Antoniazzi
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Mateusz Raczyński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Suji Park
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Houk Jang
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
| | - Adam Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Abdullah Al-Mahboob
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - Maciej R Molas
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
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6
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Li WH, Lin JD, Lo PY, Peng GH, Hei CY, Chen SY, Cheng SJ. The Key Role of Non-Local Screening in the Environment-Insensitive Exciton Fine Structures of Transition-Metal Dichalcogenide Monolayers. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:nano13111739. [PMID: 37299642 DOI: 10.3390/nano13111739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Revised: 05/21/2023] [Accepted: 05/23/2023] [Indexed: 06/12/2023]
Abstract
In this work, we present a comprehensive theoretical and computational investigation of exciton fine structures of WSe2-monolayers, one of the best-known two-dimensional (2D) transition-metal dichalcogenides (TMDs), in various dielectric-layered environments by solving the first-principles-based Bethe-Salpeter equation. While the physical and electronic properties of atomically thin nanomaterials are normally sensitive to the variation of the surrounding environment, our studies reveal that the influence of the dielectric environment on the exciton fine structures of TMD-MLs is surprisingly limited. We point out that the non-locality of Coulomb screening plays a key role in suppressing the dielectric environment factor and drastically shrinking the fine structure splittings between bright exciton (BX) states and various dark-exciton (DX) states of TMD-MLs. The intriguing non-locality of screening in 2D materials can be manifested by the measurable non-linear correlation between the BX-DX splittings and exciton-binding energies by varying the surrounding dielectric environments. The revealed environment-insensitive exciton fine structures of TMD-ML suggest the robustness of prospective dark-exciton-based optoelectronics against the inevitable variation of the inhomogeneous dielectric environment.
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Affiliation(s)
- Wei-Hua Li
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Jhen-Dong Lin
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Ping-Yuan Lo
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Guan-Hao Peng
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Ching-Yu Hei
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
| | - Shao-Yu Chen
- Center of Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan
- Center of Atomic Initiative for New Material, National Taiwan University, Taipei 106, Taiwan
| | - Shun-Jen Cheng
- Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 300, Taiwan
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7
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Koutenský P, Slobodeniuk A, Bartoš M, Trojánek F, Malý P, Kozák M. Ultrafast Dynamics of Valley-Polarized Excitons in WSe 2 Monolayer Studied by Few-Cycle Laser Pulses. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:1207. [PMID: 37049301 PMCID: PMC10096652 DOI: 10.3390/nano13071207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Revised: 03/20/2023] [Accepted: 03/27/2023] [Indexed: 06/19/2023]
Abstract
We report on the experimental investigation of the ultrafast dynamics of valley-polarized excitons in monolayer WSe2 using transient reflection spectroscopy with few-cycle laser pulses with 7 fs duration. We observe that at room temperature, the anisotropic valley population of excitons decays on two different timescales. The shorter decay time of approximately 120 fs is related to the initial hot exciton relaxation related to the fast direct recombination of excitons from the radiative zone, while the slower picosecond dynamics corresponds to valley depolarization induced by Coloumb exchange-driven transitions of excitons between two inequivalent valleys.
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Affiliation(s)
- Petr Koutenský
- Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Prague, Czech Republic
| | - Artur Slobodeniuk
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Miroslav Bartoš
- Central European Institute of Technology, Brno University of Technology, Purkyňova 656/123, 612 00 Brno, Czech Republic
| | - František Trojánek
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Petr Malý
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Martin Kozák
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
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8
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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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9
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Raiber S, Faria Junior PE, Falter D, Feldl S, Marzena P, Watanabe K, Taniguchi T, Fabian J, Schüller C. Ultrafast pseudospin quantum beats in multilayer WSe 2 and MoSe 2. Nat Commun 2022; 13:4997. [PMID: 36008400 PMCID: PMC9411176 DOI: 10.1038/s41467-022-32534-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Accepted: 08/04/2022] [Indexed: 11/09/2022] Open
Abstract
Layered van-der-Waals materials with hexagonal symmetry offer an extra degree of freedom to their electrons, the so-called valley index or valley pseudospin, which behaves conceptually like the electron spin. Here, we present investigations of excitonic transitions in mono- and multilayer WSe2 and MoSe2 materials by time-resolved Faraday ellipticity (TRFE) with in-plane magnetic fields, B∥, of up to 9 T. In monolayer samples, the measured TRFE time traces are almost independent of B∥, which confirms a close to zero in-plane exciton g factor g∥, consistent with first-principles calculations. In contrast, we observe pronounced temporal oscillations in multilayer samples for B∥ > 0. Our first-principles calculations confirm the presence of a non-zero g∥ for the multilayer samples. We propose that the oscillatory TRFE signal in the multilayer samples is caused by pseudospin quantum beats of excitons, which is a manifestation of spin- and pseudospin layer locking in the multilayer samples.
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Affiliation(s)
- Simon Raiber
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Paulo E Faria Junior
- Institut für Theoretische Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Dennis Falter
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Simon Feldl
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Petter Marzena
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Jaroslav Fabian
- Institut für Theoretische Physik, Universität Regensburg, D-93040, Regensburg, Germany
| | - Christian Schüller
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg, D-93040, Regensburg, Germany.
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10
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Blundo E, Junior PEF, Surrente A, Pettinari G, Prosnikov MA, Olkowska-Pucko K, Zollner K, Woźniak T, Chaves A, Kazimierczuk T, Felici M, Babiński A, Molas MR, Christianen PCM, Fabian J, Polimeni A. Strain-Induced Exciton Hybridization in WS_{2} Monolayers Unveiled by Zeeman-Splitting Measurements. PHYSICAL REVIEW LETTERS 2022; 129:067402. [PMID: 36018658 DOI: 10.1103/physrevlett.129.067402] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 06/09/2022] [Indexed: 06/15/2023]
Abstract
Mechanical deformations and ensuing strain are routinely exploited to tune the band gap energy and to enhance the functionalities of two-dimensional crystals. In this Letter, we show that strain leads also to a strong modification of the exciton magnetic moment in WS_{2} monolayers. Zeeman-splitting measurements under magnetic fields up to 28.5 T were performed on single, one-layer-thick WS_{2} microbubbles. The strain of the bubbles causes a hybridization of k-space direct and indirect excitons resulting in a sizable decrease in the modulus of the g factor of the ground-state exciton. These findings indicate that strain may have major effects on the way the valley number of excitons can be used to process binary information in two-dimensional crystals.
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Affiliation(s)
- Elena Blundo
- Physics Department, Sapienza University of Rome, 00185 Rome, Italy
| | - Paulo E Faria Junior
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Alessandro Surrente
- Physics Department, Sapienza University of Rome, 00185 Rome, Italy
- Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, 50-370 Wrocław, Poland
| | - Giorgio Pettinari
- Institute for Photonics and Nanotechnologies, National Research Council, 00156 Rome, Italy
| | - Mikhail A Prosnikov
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - Katarzyna Olkowska-Pucko
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Klaus Zollner
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Tomasz Woźniak
- Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, 50-370 Wrocław, Poland
| | - Andrey Chaves
- Departamento de Fisica, Universidade Federal do Ceará, 60455-900 Fortaleza, Ceará, Brazil
- Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
| | - Tomasz Kazimierczuk
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Marco Felici
- Physics Department, Sapienza University of Rome, 00185 Rome, Italy
| | - Adam Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Maciej R Molas
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Peter C M Christianen
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - Jaroslav Fabian
- Institute for Theoretical Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Antonio Polimeni
- Physics Department, Sapienza University of Rome, 00185 Rome, Italy
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11
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Bieniek M, Sadecka K, Szulakowska L, Hawrylak P. Theory of Excitons in Atomically Thin Semiconductors: Tight-Binding Approach. NANOMATERIALS (BASEL, SWITZERLAND) 2022; 12:1582. [PMID: 35564291 PMCID: PMC9104105 DOI: 10.3390/nano12091582] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2022] [Revised: 04/24/2022] [Accepted: 04/26/2022] [Indexed: 02/01/2023]
Abstract
Atomically thin semiconductors from the transition metal dichalcogenide family are materials in which the optical response is dominated by strongly bound excitonic complexes. Here, we present a theory of excitons in two-dimensional semiconductors using a tight-binding model of the electronic structure. In the first part, we review extensive literature on 2D van der Waals materials, with particular focus on their optical response from both experimental and theoretical points of view. In the second part, we discuss our ab initio calculations of the electronic structure of MoS2, representative of a wide class of materials, and review our minimal tight-binding model, which reproduces low-energy physics around the Fermi level and, at the same time, allows for the understanding of their electronic structure. Next, we describe how electron-hole pair excitations from the mean-field-level ground state are constructed. The electron-electron interactions mix the electron-hole pair excitations, resulting in excitonic wave functions and energies obtained by solving the Bethe-Salpeter equation. This is enabled by the efficient computation of the Coulomb matrix elements optimized for two-dimensional crystals. Next, we discuss non-local screening in various geometries usually used in experiments. We conclude with a discussion of the fine structure and excited excitonic spectra. In particular, we discuss the effect of band nesting on the exciton fine structure; Coulomb interactions; and the topology of the wave functions, screening and dielectric environment. Finally, we follow by adding another layer and discuss excitons in heterostructures built from two-dimensional semiconductors.
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Affiliation(s)
- Maciej Bieniek
- Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (K.S.); (L.S.); (P.H.)
- Department of Theoretical Physics, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
- Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Katarzyna Sadecka
- Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (K.S.); (L.S.); (P.H.)
- Department of Theoretical Physics, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
| | - Ludmiła Szulakowska
- Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (K.S.); (L.S.); (P.H.)
| | - Paweł Hawrylak
- Department of Physics, University of Ottawa, Ottawa, ON K1N 6N5, Canada; (K.S.); (L.S.); (P.H.)
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12
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Katznelson S, Cohn B, Sufrin S, Amit T, Mukherjee S, Kleiner V, Mohapatra P, Patsha A, Ismach A, Refaely-Abramson S, Hasman E, Koren E. Bright excitonic multiplexing mediated by dark exciton transition in two-dimensional TMDCs at room temperature. MATERIALS HORIZONS 2022; 9:1089-1098. [PMID: 35083477 DOI: 10.1039/d1mh01186c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
2D-semiconductors with strong light-matter interaction are attractive materials for integrated and tunable optical devices. Here, we demonstrate room-temperature wavelength multiplexing of the two-primary bright excitonic channels (Ab-, Bb-) in monolayer transition metal dichalcogenides (TMDs) arising from a dark exciton mediated transition. We present how tuning dark excitons via an out-of-plane electric field cedes the system equilibrium from one excitonic channel to the other, encoding the field polarization into wavelength information. In addition, we demonstrate how such exciton multiplexing is dictated by thermal-scattering by performing temperature dependent photoluminescence measurements. Finally, we demonstrate experimentally and theoretically how excitonic mixing can explain preferable decay through dark states in MoX2 in comparison with WX2 monolayers. Such field polarization-based manipulation of excitonic transitions can pave the way for novel photonic device architectures.
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Affiliation(s)
- Shaul Katznelson
- Nanoscale Electronic Materials and Devices Laboratory, Faculty of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Bar Cohn
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
- Atomic-Scale Photonics Laboratory, Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Shmuel Sufrin
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
- Atomic-Scale Photonics Laboratory, Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Tomer Amit
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Subhrajit Mukherjee
- Nanoscale Electronic Materials and Devices Laboratory, Faculty of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
| | - Vladimir Kleiner
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
- Atomic-Scale Photonics Laboratory, Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Pranab Mohapatra
- Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel
| | - Avinash Patsha
- Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel
| | - Ariel Ismach
- Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel
| | - Sivan Refaely-Abramson
- Department of Molecular Chemistry and Materials Science, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Erez Hasman
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
- Atomic-Scale Photonics Laboratory, Faculty of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel
| | - Elad Koren
- Nanoscale Electronic Materials and Devices Laboratory, Faculty of Materials Science and Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
- Russell Berrie Nanotechnology Institute, and Helen Diller Quantum Center, Technion - Israel Institute of Technology, Haifa 3200003, Israel
- The Nancy and Stephen Grand Technion Energy Program, Technion - Israel Institute of Technology, Haifa 3200003, Israel
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13
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Jadczak J, Glazov M, Kutrowska-Girzycka J, Schindler JJ, Debus J, Ho CH, Watanabe K, Taniguchi T, Bayer M, Bryja L. Upconversion of Light into Bright Intravalley Excitons via Dark Intervalley Excitons in hBN-Encapsulated WSe 2 Monolayers. ACS NANO 2021; 15:19165-19174. [PMID: 34735768 PMCID: PMC8717626 DOI: 10.1021/acsnano.1c08286] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 10/29/2021] [Indexed: 05/19/2023]
Abstract
Semiconducting monolayers of transition-metal dichalcogenides are outstanding platforms to study both electronic and phononic interactions as well as intra- and intervalley excitons and trions. These excitonic complexes are optically either active (bright) or inactive (dark) due to selection rules from spin or momentum conservation. Exploring ways of brightening dark excitons and trions has strongly been pursued in semiconductor physics. Here, we report on a mechanism in which a dark intervalley exciton upconverts light into a bright intravalley exciton in hBN-encapsulated WSe2 monolayers. Excitation spectra of upconverted photoluminescence reveals resonances at energies 34.5 and 46.0 meV below the neutral exciton in the nominal WSe2 transparency range. The required energy gains are theoretically explained by cooling of resident electrons or by exciton scattering with Λ- or K-valley phonons. Accordingly, an elevated temperature and a moderate concentration of resident electrons are necessary for observing the upconversion resonances. The interaction process observed between the inter- and intravalley excitons elucidates the importance of dark excitons for the optics of two-dimensional materials.
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Affiliation(s)
- Joanna Jadczak
- Department
of Experimental Physics, Wrocław University
of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
- (J.J.)
| | | | - Joanna Kutrowska-Girzycka
- Department
of Experimental Physics, Wrocław University
of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
| | | | - Joerg Debus
- Experimental
Physics 2, TU Dortmund University, 44227 Dortmund, Germany
| | - Ching-Hwa Ho
- Graduate
Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 106, Taiwan
| | - Kenji Watanabe
- National
Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Takashi Taniguchi
- National
Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Manfred Bayer
- Experimental
Physics 2, TU Dortmund University, 44227 Dortmund, Germany
| | - Leszek Bryja
- Department
of Experimental Physics, Wrocław University
of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
- (L.B.)
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14
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Zinkiewicz M, Woźniak T, Kazimierczuk T, Kapuscinski P, Oreszczuk K, Grzeszczyk M, Bartoš M, Nogajewski K, Watanabe K, Taniguchi T, Faugeras C, Kossacki P, Potemski M, Babiński A, Molas MR. Excitonic Complexes in n-Doped WS 2 Monolayer. NANO LETTERS 2021; 21:2519-2525. [PMID: 33683895 PMCID: PMC7995249 DOI: 10.1021/acs.nanolett.0c05021] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/22/2021] [Indexed: 05/25/2023]
Abstract
We investigate the origin of emission lines apparent in the low-temperature photoluminescence spectra of n-doped WS2 monolayer embedded in hexagonal BN layers using external magnetic fields and first-principles calculations. Apart from the neutral A exciton line, all observed emission lines are related to the negatively charged excitons. Consequently, we identify emissions due to both the bright (singlet and triplet) and dark (spin- and momentum-forbidden) negative trions as well as the phonon replicas of the latter optically inactive complexes. The semidark trions and negative biexcitons are distinguished. On the basis of their experimentally extracted and theoretically calculated g-factors, we identify three distinct families of emissions due to exciton complexes in WS2: bright, intravalley, and intervalley dark. The g-factors of the spin-split subbands in both the conduction and valence bands are also determined.
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Affiliation(s)
- Małgorzata Zinkiewicz
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Tomasz Woźniak
- Department
of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego
27, 50-370 Wrocław, Poland
| | - Tomasz Kazimierczuk
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Piotr Kapuscinski
- Laboratoire
National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
- Department
of Experimental Physics, Wrocław University
of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland
| | - Kacper Oreszczuk
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Magdalena Grzeszczyk
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Miroslav Bartoš
- Laboratoire
National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
- Central
European Institute of Technology, Brno University
of Technology, Purkyňova
656/123, 612 00 Brno, Czech Republic
| | - Karol Nogajewski
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Kenji Watanabe
- Research
Center for Functional Materials, National
Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Takashi Taniguchi
- International
Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - Clement Faugeras
- Laboratoire
National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
| | - Piotr Kossacki
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Marek Potemski
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
- Laboratoire
National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
| | - Adam Babiński
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
| | - Maciej R. Molas
- Institute
of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland
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15
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Rivera P, He M, Kim B, Liu S, Rubio-Verdú C, Moon H, Mennel L, Rhodes DA, Yu H, Taniguchi T, Watanabe K, Yan J, Mandrus DG, Dery H, Pasupathy A, Englund D, Hone J, Yao W, Xu X. Intrinsic donor-bound excitons in ultraclean monolayer semiconductors. Nat Commun 2021; 12:871. [PMID: 33558508 PMCID: PMC7870970 DOI: 10.1038/s41467-021-21158-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 01/11/2021] [Indexed: 01/30/2023] Open
Abstract
The monolayer transition metal dichalcogenides are an emergent semiconductor platform exhibiting rich excitonic physics with coupled spin-valley degree of freedom and optical addressability. Here, we report a new series of low energy excitonic emission lines in the photoluminescence spectrum of ultraclean monolayer WSe2. These excitonic satellites are composed of three major peaks with energy separations matching known phonons, and appear only with electron doping. They possess homogenous spatial and spectral distribution, strong power saturation, and anomalously long population (>6 µs) and polarization lifetimes (>100 ns). Resonant excitation of the free inter- and intravalley bright trions leads to opposite optical orientation of the satellites, while excitation of the free dark trion resonance suppresses the satellites' photoluminescence. Defect-controlled crystal synthesis and scanning tunneling microscopy measurements provide corroboration that these features are dark excitons bound to dilute donors, along with associated phonon replicas. Our work opens opportunities to engineer homogenous single emitters and explore collective quantum optical phenomena using intrinsic donor-bound excitons in ultraclean 2D semiconductors.
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Affiliation(s)
- Pasqual Rivera
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Minhao He
- Department of Physics, University of Washington, Seattle, WA, 98195, USA
| | - Bumho Kim
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Song Liu
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | | | - Hyowon Moon
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Lukas Mennel
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Daniel A Rhodes
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA
| | - Hongyi Yu
- Department of Physics, University of Hong Kong, and HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Kenji Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - Jiaqiang Yan
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA
| | - David G Mandrus
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN, 37996, USA
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, 37996, USA
| | - Hanan Dery
- Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY, 14627, USA
| | - Abhay Pasupathy
- Department of Physics, Columbia University, New York, NY, 10027, USA
| | - Dirk Englund
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, 10027, USA.
| | - Wang Yao
- Department of Physics, University of Hong Kong, and HKU-UCAS Joint Institute of Theoretical and Computational Physics at Hong Kong, Hong Kong, China.
| | - Xiaodong Xu
- Department of Physics, University of Washington, Seattle, WA, 98195, USA.
- Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98195, USA.
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16
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Investigations of Electron-Electron and Interlayer Electron-Phonon Coupling in van der Waals hBN/WSe 2/hBN Heterostructures by Photoluminescence Excitation Experiments. MATERIALS 2021; 14:ma14020399. [PMID: 33467435 PMCID: PMC7830124 DOI: 10.3390/ma14020399] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 01/10/2021] [Accepted: 01/11/2021] [Indexed: 11/17/2022]
Abstract
Monolayers of transition metal dichalcogenides (TMDs) with their unique physical properties are very promising for future applications in novel electronic devices. In TMDs monolayers, strong and opposite spin splittings of the energy gaps at the K points allow for exciting carriers with various combinations of valley and spin indices using circularly polarized light, which can further be used in spintronics and valleytronics. The physical properties of van der Waals heterostructures composed of TMDs monolayers and hexagonal boron nitride (hBN) layers significantly depend on different kinds of interactions. Here, we report on observing both a strong increase in the emission intensity as well as a preservation of the helicity of the excitation light in the emission from hBN/WSe2/hBN heterostructures related to interlayer electron-phonon coupling. In combined low-temperature (T = 7 K) reflectivity contrast and photoluminescence excitation experiments, we find that the increase in the emission intensity is attributed to a double resonance, where the laser excitation and the combined Raman mode A'1 (WSe2) + ZO (hBN) are in resonance with the excited (2s) and ground (1s) states of the A exciton in a WSe2 monolayer. In reference to the 2s state, our interpretation is in contrast with previous reports, in which this state has been attributed to the hybrid exciton state existing only in the hBN-encapsulated WSe2 monolayer. Moreover, we observe that the electron-phonon coupling also enhances the helicity preservation of the exciting light in the emission of all observed excitonic complexes. The highest helicity preservation of more than 60% is obtained in the emission of the neutral biexciton and negatively charged exciton (trion) in its triplet state. Additionally, to the best of our knowledge, the strongly intensified emission of the neutral biexciton XX0 at double resonance condition is observed for the first time.
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17
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Neuhaus J, Liebscher SC, Meckbach L, Stroucken T, Koch SW. Microscopic Coulomb interaction in transition-metal dichalcogenides. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 33:035301. [PMID: 32906108 DOI: 10.1088/1361-648x/abb681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/23/2020] [Accepted: 09/09/2020] [Indexed: 06/11/2023]
Abstract
The quasi-two dimensional Coulomb interaction potential in transition metal dichalcogenides is determined using the Kohn-Sham wave functions obtained fromab initiocalculations. An effective form factor is derived that accounts for the finite extension of the wave functions in the direction perpendicular to the material layer. The resulting Coulomb matrix elements are used in microscopic calculations based on the Dirac Bloch equations yielding an efficient method to calculate the band gap and the opto-electronic material properties in different environments and under various excitation conditions.
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Affiliation(s)
- J Neuhaus
- Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany
| | - S C Liebscher
- Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany
| | - L Meckbach
- Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany
| | - T Stroucken
- Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany
| | - S W Koch
- Department of Physics and Material Sciences Center, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany
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18
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Zinkiewicz M, Slobodeniuk AO, Kazimierczuk T, Kapuściński P, Oreszczuk K, Grzeszczyk M, Bartos M, Nogajewski K, Watanabe K, Taniguchi T, Faugeras C, Kossacki P, Potemski M, Babiński A, Molas MR. Neutral and charged dark excitons in monolayer WS 2. NANOSCALE 2020; 12:18153-18159. [PMID: 32853305 DOI: 10.1039/d0nr04243a] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Low temperature and polarization resolved magneto-photoluminescence experiments are used to investigate the properties of dark excitons and dark trions in a monolayer of WS2 encapsulated in hexagonal BN (hBN). We find that this system is an n-type doped semiconductor and that dark trions dominate the emission spectrum. In line with previous studies on WSe2, we identify the Coulomb exchange interaction coupled neutral dark and grey excitons through their polarization properties, while an analogous effect is not observed for dark trions. Applying the magnetic field in both perpendicular and parallel configurations with respect to the monolayer plane, we determine the g-factor of dark trions to be g ∼ -8.6. Their decay rate is close to 0.5 ns, more than 2 orders of magnitude longer than that of bright excitons.
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Affiliation(s)
- M Zinkiewicz
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - A O Slobodeniuk
- Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, Praha 2 CZ-121 16, Czech Republic
| | - T Kazimierczuk
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - P Kapuściński
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France and Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, ul. Wybrzeże Wyspiańskiego 27, 50-370 Wrocław, Poland
| | - K Oreszczuk
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - M Grzeszczyk
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - M Bartos
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France and Central European Institute of Technology, Brno University of Technology, Purkyňova 656/123, 612 00 Brno, Czech Republic
| | - K Nogajewski
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - K Watanabe
- Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - C Faugeras
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
| | - P Kossacki
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - M Potemski
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland. and Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25, avenue des Martyrs, 38042 Grenoble, France
| | - A Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
| | - M R Molas
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warsaw, Poland.
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Robert C, Han B, Kapuscinski P, Delhomme A, Faugeras C, Amand T, Molas MR, Bartos M, Watanabe K, Taniguchi T, Urbaszek B, Potemski M, Marie X. Measurement of the spin-forbidden dark excitons in MoS 2 and MoSe 2 monolayers. Nat Commun 2020; 11:4037. [PMID: 32788704 PMCID: PMC7423942 DOI: 10.1038/s41467-020-17608-4] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 07/08/2020] [Indexed: 11/13/2022] Open
Abstract
Excitons with binding energies of a few hundreds of meV control the optical properties of transition metal dichalcogenide monolayers. Knowledge of the fine structure of these excitons is therefore essential to understand the optoelectronic properties of these 2D materials. Here we measure the exciton fine structure of MoS2 and MoSe2 monolayers encapsulated in boron nitride by magneto-photoluminescence spectroscopy in magnetic fields up to 30 T. The experiments performed in transverse magnetic field reveal a brightening of the spin-forbidden dark excitons in MoS2 monolayer: we find that the dark excitons appear at 14 meV below the bright ones. Measurements performed in tilted magnetic field provide a conceivable description of the neutral exciton fine structure. The experimental results are in agreement with a model taking into account the effect of the exchange interaction on both the bright and dark exciton states as well as the interaction with the magnetic field.
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Affiliation(s)
- C Robert
- University of Toulouse, INSA-CNRS-UPS, LPCNO, 135 Av. Rangueil, 31077, Toulouse, France.
| | - B Han
- University of Toulouse, INSA-CNRS-UPS, LPCNO, 135 Av. Rangueil, 31077, Toulouse, France.
| | - P Kapuscinski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 38042, Grenoble, France
- Department of Experimental Physics, Faculty of Fundamental Problems of Technology, Wrocław University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370, Wrocław, Poland
| | - A Delhomme
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 38042, Grenoble, France
| | - C Faugeras
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 38042, Grenoble, France.
| | - T Amand
- University of Toulouse, INSA-CNRS-UPS, LPCNO, 135 Av. Rangueil, 31077, Toulouse, France
| | - M R Molas
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093, Warsaw, Poland
| | - M Bartos
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 38042, Grenoble, France
- Central European Institute of Technology, Brno University of Technology, Purkynova 656/123, 61200, Brno, Czech Republic
| | - K Watanabe
- National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, Tsukuba, Ibaraki, 305-0044, Japan
| | - B Urbaszek
- University of Toulouse, INSA-CNRS-UPS, LPCNO, 135 Av. Rangueil, 31077, Toulouse, France
| | - M Potemski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 38042, Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093, Warsaw, Poland
| | - X Marie
- University of Toulouse, INSA-CNRS-UPS, LPCNO, 135 Av. Rangueil, 31077, Toulouse, France
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20
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Liu E, van Baren J, Liang CT, Taniguchi T, Watanabe K, Gabor NM, Chang YC, Lui CH. Multipath Optical Recombination of Intervalley Dark Excitons and Trions in Monolayer WSe_{2}. PHYSICAL REVIEW LETTERS 2020; 124:196802. [PMID: 32469553 DOI: 10.1103/physrevlett.124.196802] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Accepted: 03/24/2020] [Indexed: 06/11/2023]
Abstract
Excitons and trions (or exciton polarons) in transition metal dichalcogenides (TMDs) are known to decay predominantly through intravalley transitions. Electron-hole recombination across different valleys can also play a significant role in the excitonic dynamics, but intervalley transitions are rarely observed in monolayer TMDs, because they violate the conservation of momentum. Here we reveal the intervalley recombination of dark excitons and trions through more than one path in monolayer WSe_{2}. We observe the intervalley dark excitons, which can recombine by the assistance of defect scattering or chiral-phonon emission. We also reveal that a trion can decay in two distinct paths-through intravalley or intervalley electron-hole recombination-into two different final valley states. Although these two paths are energy degenerate, we can distinguish them by lifting the valley degeneracy under a magnetic field. In addition, the intra- and inter-valley trion transitions are coupled to zone-center and zone-corner chiral phonons, respectively, to produce distinct phonon replicas. The observed multipath optical decays of dark excitons and trions provide insight into the internal quantum structure of trions and the complex excitonic interactions with defects and chiral phonons in monolayer valley semiconductors.
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Affiliation(s)
- Erfu Liu
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Jeremiah van Baren
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
| | - Ching-Tarng Liang
- Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Takashi Taniguchi
- International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science (NIMS), 1-1 Namiki Tsukuba, Ibaraki 305-0044, Japan
| | - Nathaniel M Gabor
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
- Canadian Institute for Advanced Research, MaRS Centre West Tower, 661 University Avenue, Toronto, Ontario ON M5G 1M1, Canada
| | - Yia-Chung Chang
- Research Center for Applied Sciences, Academia Sinica, Taipei 11529, Taiwan
| | - Chun Hung Lui
- Department of Physics and Astronomy, University of California, Riverside, California 92521, USA
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Molas MR, Slobodeniuk AO, Nogajewski K, Bartos M, Bala Ł, Babiński A, Watanabe K, Taniguchi T, Faugeras C, Potemski M. Energy Spectrum of Two-Dimensional Excitons in a Nonuniform Dielectric Medium. PHYSICAL REVIEW LETTERS 2019; 123:136801. [PMID: 31697524 DOI: 10.1103/physrevlett.123.136801] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Indexed: 06/10/2023]
Abstract
We demonstrate that, in monolayers (MLs) of semiconducting transition metal dichalcogenides, the s-type Rydberg series of excitonic states follows a simple energy ladder: ε_{n}=-Ry^{*}/(n+δ)^{2}, n=1,2,…, in which Ry^{*} is very close to the Rydberg energy scaled by the dielectric constant of the medium surrounding the ML and by the reduced effective electron-hole mass, whereas the ML polarizability is accounted for only by δ. This is justified by the analysis of experimental data on excitonic resonances, as extracted from magneto-optical measurements of a high-quality WSe_{2} ML encapsulated in hexagonal boron nitride (hBN), and well reproduced with an analytically solvable Schrödinger equation when approximating the electron-hole potential in the form of a modified Kratzer potential. Applying our convention to other MoSe_{2}, WS_{2}, MoS_{2} MLs encapsulated in hBN, we estimate an apparent magnitude of δ for each of the studied structures. Intriguingly, δ is found to be close to zero for WSe_{2} as well as for MoS_{2} monolayers, what implies that the energy ladder of excitonic states in these two-dimensional structures resembles that of Rydberg states of a three-dimensional hydrogen atom.
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Affiliation(s)
- M R Molas
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - A O Slobodeniuk
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - K Nogajewski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - M Bartos
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Central European Institute of Technology, Brno University of Technology, Purkyňova 656/123, 61200 Brno, Czech Republic
| | - Ł Bala
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - A Babiński
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
| | - K Watanabe
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - T Taniguchi
- National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
| | - C Faugeras
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
| | - M Potemski
- Laboratoire National des Champs Magnétiques Intenses, CNRS-UGA-UPS-INSA-EMFL, 25 avenue des Martyrs, 38042 Grenoble, France
- Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Pasteura 5, 02-093 Warszawa, Poland
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