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Del Águila AG, Wong YR, Wadgaonkar I, Fieramosca A, Liu X, Vaklinova K, Dal Forno S, Do TTH, Wei HY, Watanabe K, Taniguchi T, Novoselov KS, Koperski M, Battiato M, Xiong Q. Ultrafast exciton fluid flow in an atomically thin MoS 2 semiconductor. Nat Nanotechnol 2023; 18:1012-1019. [PMID: 37524907 DOI: 10.1038/s41565-023-01438-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 06/01/2023] [Indexed: 08/02/2023]
Abstract
Excitons (coupled electron-hole pairs) in semiconductors can form collective states that sometimes exhibit spectacular nonlinear properties. Here, we show experimental evidence of a collective state of short-lived excitons in a direct-bandgap, atomically thin MoS2 semiconductor whose propagation resembles that of a classical liquid as suggested by the nearly uniform photoluminescence through the MoS2 monolayer regardless of crystallographic defects and geometric constraints. The exciton fluid flows over ultralong distances (at least 60 μm) at a speed of ~1.8 × 107 m s-1 (~6% the speed of light). The collective phase emerges above a critical laser power, in the absence of free charges and below a critical temperature (usually Tc ≈ 150 K) approaching room temperature in hexagonal-boron-nitride-encapsulated devices. Our theoretical simulations suggest that momentum is conserved and local equilibrium is achieved among excitons; both these features are compatible with a fluid dynamics description of the exciton transport.
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Affiliation(s)
- Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
| | - Yi Ren Wong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Indrajit Wadgaonkar
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Antonio Fieramosca
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Xue Liu
- Institutes of Physical Science and Information Technology, Anhui University, Hefei, P.R. China
| | - Kristina Vaklinova
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
| | - Stefano Dal Forno
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - T Thu Ha Do
- Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore, Republic of Singapore
| | - Ho Yi Wei
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Department of Physics, National University of Singapore, Singapore, Singapore
| | - K Watanabe
- National Institute for Materials Science, Tsukuba, Japan
| | - T Taniguchi
- National Institute for Materials Science, Tsukuba, Japan
| | - Kostya S Novoselov
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore
| | - Maciej Koperski
- Institute for Functional Intelligent Materials, National University of Singapore, Singapore, Singapore
- Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore
| | - Marco Battiato
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore
| | - Qihua Xiong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, P.R. China.
- Frontier Science Center for Quantum Information, Beijing, P.R. China.
- Collaborative Innovation Center of Quantum Matter, Beijing, P.R. China.
- Beijing Academy of Quantum Information Sciences, Beijing, P.R. China.
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2
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Yin T, Ulman KA, Liu S, Granados Del Águila A, Huang Y, Zhang L, Serra M, Sedmidubsky D, Sofer Z, Quek SY, Xiong Q. Chiral Phonons and Giant Magneto-Optical Effect in CrBr 3 2D Magnet. Adv Mater 2021; 33:e2101618. [PMID: 34302389 DOI: 10.1002/adma.202101618] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2021] [Revised: 06/20/2021] [Indexed: 06/13/2023]
Abstract
Phonons with chirality determine the optical helicity of inelastic light scattering processes due to their nonzero angular momentum. Here it is shown that 2D magnetic CrBr3 hosts chiral phonons at the Brillouin-zone center. These chiral phonons are linear combinations of the doubly-degenerate Eg phonons, and the phonon eigenmodes exhibit clockwise and counterclockwise rotational vibrations corresponding to angular momenta of l = ± 1. Such Eg chiral phonons completely switch the polarization of incident circularly polarized light. On the other hand, the non-degenerate non-chiral Ag phonons display a giant magneto-optical effect under an external out-of-plane magnetic field, rotating the plane of polarization of the scattered linearly polarized light. The corresponding degree of polarization of the scattered light changes from 91% to -68% as the magnetic field strength increases from 0 to 5 T. In contrast, the chiral Eg modes display no field dependence. The results lay a foundation for the study of phonon chirality and magneto-optical phenomena in 2D magnetic materials, as well as their related applications, such as the phonon Hall effect, topological photonics, and Raman lasing.
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Affiliation(s)
- Tingting Yin
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - Kanchan Ajit Ulman
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
| | - Sheng Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - Yuqing Huang
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore
| | - Lifa Zhang
- NNU-SULI Thermal Energy Research Center and Center for Quantum Transport and Thermal Energy Science, School of Physics and Technology, Nanjing Normal University, Nanjing, China
| | - Marco Serra
- University of Chemistry and Technology Prague, Technicka 5, Prague, 16628, Czech Republic
| | - David Sedmidubsky
- University of Chemistry and Technology Prague, Technicka 5, Prague, 16628, Czech Republic
| | - Zdenek Sofer
- University of Chemistry and Technology Prague, Technicka 5, Prague, 16628, Czech Republic
| | - Su Ying Quek
- Centre for Advanced 2D Materials, National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore
- Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542, Singapore
- NUS Graduate School, Integrative Sciences and Engineering Programme, National University of Singapore, Singapore, 117456, Singapore
- Department of Materials Science and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117575, Singapore
| | - Qihua Xiong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing, 100084, P. R. China
- Beijing Academy of Quantum Information Sciences, Beijing, 100193, P. R. China
- Beijing Innovation Center for Future Chips, Tsinghua University, Beijing, 100084, P. R. China
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3
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Liu S, Granados Del Águila A, Bhowmick D, Gan CK, Thu Ha Do T, Prosnikov MA, Sedmidubský D, Sofer Z, Christianen PCM, Sengupta P, Xiong Q. Direct Observation of Magnon-Phonon Strong Coupling in Two-Dimensional Antiferromagnet at High Magnetic Fields. Phys Rev Lett 2021; 127:097401. [PMID: 34506201 DOI: 10.1103/physrevlett.127.097401] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2021] [Accepted: 07/30/2021] [Indexed: 05/08/2023]
Abstract
We report the direct observation of strong coupling between magnons and phonons in a two-dimensional antiferromagnetic semiconductor FePS_{3}, via magneto-Raman spectroscopy at magnetic fields up to 30 Tesla. A Raman-active magnon at 121 cm^{-1} is identified through Zeeman splitting in an applied magnetic field. At a field-driven resonance with a nearby phonon mode, a hybridized magnon-phonon quasiparticle is formed due to strong coupling between the two modes. We develop a microscopic model of the strong coupling in the two-dimensional magnetic lattice, which enables us to elucidate the nature of the emergent quasiparticle. Our polarized Raman results directly show that the magnons transfer their spin angular momentum to the phonons and generate phonon spin through the strong coupling.
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Affiliation(s)
- Sheng Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Dhiman Bhowmick
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Chee Kwan Gan
- Institute of High Performance Computing, 1 Fusionopolis Way, 16-16 Connexis, Singapore 138632
| | - T Thu Ha Do
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - M A Prosnikov
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, Netherlands
| | - David Sedmidubský
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic
| | - Zdenek Sofer
- Department of Inorganic Chemistry, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6, Czech Republic
| | - Peter C M Christianen
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, Netherlands
| | - Pinaki Sengupta
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Qihua Xiong
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
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4
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Tedeschi D, Fonseka HA, Blundo E, Granados Del Águila A, Guo Y, Tan HH, Christianen PCM, Jagadish C, Polimeni A, De Luca M. Hole and Electron Effective Masses in Single InP Nanowires with a Wurtzite-Zincblende Homojunction. ACS Nano 2020; 14:11613-11622. [PMID: 32865391 DOI: 10.1021/acsnano.0c04174] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The formation of wurtzite (WZ) phase in III-V nanowires (NWs) such as GaAs and InP is a complication hindering the growth of pure-phase NWs, but it can also be exploited to form NW homostructures consisting of alternate zincblende (ZB) and WZ segments. This leads to different forms of nanostructures, such as crystal-phase superlattices and quantum dots. Here, we investigate the electronic properties of the simplest, yet challenging, of such homostructures: InP NWs with a single homojunction between pure ZB and WZ segments. Polarization-resolved microphotoluminescence (μ-PL) measurements on single NWs provide a tool to gain insights into the interplay between NW geometry and crystal phase. We also exploit this homostructure to simultaneously measure effective masses of charge carriers and excitons in ZB and WZ InP NWs, reliably. Magneto-μ-PL measurements carried out on individual NWs up to 29 T at 77 K allow us to determine the free exciton reduced masses of the ZB and WZ crystal phases, showing the heavier character of the WZ phase, and to deduce the effective mass of electrons in ZB InP NWs (me= 0.080 m0). Finally, we obtain the reduced mass of light-hole excitons in WZ InP by probing the second optically permitted transition Γ7C ↔ Γ7uV with magneto-μ-PL measurements carried out at room temperature. This information is used to extract the experimental light-hole effective mass in WZ InP, which is found to be mlh = 0.26 m0, a value much smaller than the one of the heavy hole mass. Besides being a valuable test for band structure calculations, the knowledge of carrier masses in WZ and ZB InP is important in view of the optimization of the efficiency of solar cells, which is one of the main applications of InP NWs.
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Affiliation(s)
- Davide Tedeschi
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 2, 00185 Roma, Italy
| | - H Aruni Fonseka
- Department of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Elena Blundo
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 2, 00185 Roma, Italy
| | - Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Yanan Guo
- Department of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Hark H Tan
- Department of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- ARC Centre of Excellence for Transformative Meta-Optical Systems, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML - EMFL), Radboud University, Toernooiveld 7, NL-6525 ED Nijmegen, The Netherlands
| | - Chennupati Jagadish
- Department of Electronic Materials Engineering, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
- ARC Centre of Excellence for Transformative Meta-Optical Systems, Research School of Physics, The Australian National University, Canberra, Australian Capital Territory 2601, Australia
| | - Antonio Polimeni
- Dipartimento di Fisica, Sapienza Università di Roma, Piazzale A. Moro 2, 00185 Roma, Italy
| | - Marta De Luca
- Department of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel, Switzerland
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5
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Liu S, Granados Del Águila A, Liu X, Zhu Y, Han Y, Chaturvedi A, Gong P, Yu H, Zhang H, Yao W, Xiong Q. Room-Temperature Valley Polarization in Atomically Thin Semiconductors via Chalcogenide Alloying. ACS Nano 2020; 14:9873-9883. [PMID: 32806059 DOI: 10.1021/acsnano.0c02703] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Room-temperature manipulation and processing of information encoded in the electronic valley pseudospin and spin degrees of freedoms lie at the heart of the next technological quantum revolution. In atomically thin layers of transition-metal dichalcogenides (TMDs) with hexagonal lattices, valley-polarized excitations and valley quantum coherence can be generated by simply shining with adequately polarized light. In turn, the polarization states of light can induce topological Hall currents in the absence of an external magnetic field, which underlies the fundamental principle of opto-valleytronics devices. However, demonstration of optical generation of valley polarization at room temperature has remained challenging and not well understood. Here, we demonstrate control of strong valley polarization (valley quantum coherence) at room temperature of up to ∼50% (∼20%) by strategically designing Coulomb forces and spin-orbit interactions in atomically thin TMDs via chalcogenide alloying. We show that tailor making the carrier density and the relative order between optically active (bright) and forbidden (dark) states by key variations on the chalcogenide atom ratio allows full control of valley pseudospin dynamics. Our findings set a comprehensive approach for intrinsic and efficient manipulation of valley pseudospin and spin degree of freedom toward realistic opto-valleytronics devices.
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Affiliation(s)
- Sheng Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Xue Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
| | - Yihan Zhu
- Advance Membrane and Porous Materials Center, Division of Physical and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
- Center for Electron Microscopy and State Key Laboratory Breeding Base of Green Chemistry Synthesis Technology, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - Yu Han
- Advance Membrane and Porous Materials Center, Division of Physical and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Saudi Arabia
| | - Apoorva Chaturvedi
- School of Material Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore
| | - Pu Gong
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Hongyi Yu
- Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing and School of Physics and Astronomy, Sun Yat-Sen University (Zhuhai Campus), Zhuhai 519082, China
| | - Hua Zhang
- Department of Chemistry and Hong Kong Branch of National Precious Metals Material Engineering Research Centre (NPMM), City University of Hong Kong, Hong Kong, China
| | - Wang Yao
- Department of Physics and Center of Theoretical and Computational Physics, University of Hong Kong, Hong Kong, China
| | - Qihua Xiong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore
- State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics, Tsinghua University, Beijing 100084, China
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6
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Do TTH, Granados Del Águila A, Zhang D, Xing J, Liu S, Prosnikov MA, Gao W, Chang K, Christianen PCM, Xiong Q. Bright Exciton Fine-Structure in Two-Dimensional Lead Halide Perovskites. Nano Lett 2020; 20:5141-5148. [PMID: 32459491 DOI: 10.1021/acs.nanolett.0c01364] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The fast-growing field of atomically thin semiconductors urges a new understanding of two-dimensional excitons, which entirely determine their optical responses. Here, taking layered lead halide perovskites as an example of unconventional two-dimensional semiconductors, by means of versatile optical spectroscopy measurements, we resolve fine-structure splitting of bright excitons of up to ∼2 meV, which is among the largest values in two-dimensional semiconducting systems. The large fine-structure splitting is attributed to the strong electron-hole exchange interaction in layered perovskites, which is proven by the optical emission in high magnetic fields of up to 30 T. Furthermore, we determine the g-factors for these bright excitons as ∼+1.8. Our findings suggest layered lead halide perovskites are an ideal platform for studying exciton spin-physics in atomically thin semiconductors that will pave the way toward exciton manipulation for novel device applications.
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Affiliation(s)
- T Thu Ha Do
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Dong Zhang
- SKLSM, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912 Beijing, 100083, China
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jun Xing
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - Sheng Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
| | - M A Prosnikov
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - Weibo Gao
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
- MajuLab, International Joint Research Unit UMI 3654, CNRS, Université Côte d'Azur, Sorbonne Université, National University of Singapore, Nanyang Technological University, Singapore 637371
| | - Kai Chang
- SKLSM, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912 Beijing, 100083, China
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing 100049, China
- Beijing Academy of Quantum Information Sciences, Beijing 100193, China
| | - Peter C M Christianen
- High Field Magnet Laboratory, HFML-EMFL, Radboud University, 6525 ED Nijmegen, The Netherlands
| | - Qihua Xiong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371
- MajuLab, International Joint Research Unit UMI 3654, CNRS, Université Côte d'Azur, Sorbonne Université, National University of Singapore, Nanyang Technological University, Singapore 637371
- State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China
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7
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Granados Del Águila A, Liu S, Do TTH, Lai Z, Tran TH, Krupp SR, Gong ZR, Zhang H, Yao W, Xiong Q. Linearly Polarized Luminescence of Atomically Thin MoS 2 Semiconductor Nanocrystals. ACS Nano 2019; 13:13006-13014. [PMID: 31577129 DOI: 10.1021/acsnano.9b05656] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Atomically thin layers of transition-metal dichalcogenides semiconductors, such as MoS2, exhibit strong and circularly polarized light emission due to inherent crystal symmetries, pronounced spin-orbit coupling, and out-of-plane dielectric and spatial confinement. While the layer-by-layer confinement is well-understood, the understanding of the impact of in-plane quantization in their optical spectrum is far behind. Here, we report the optical properties of atomically thin MoS2 colloidal semiconductor nanocrystals. In addition to the spatial-confinement effect leading to their blue wavelength emission, the high quality of our MoS2 nanocrystals is revealed by narrow photoluminescence, which allows us to resolve multiple optically active transitions, originating from quantum-confined excitons (coupled electron-hole pairs). Surprisingly, in stark contrast to monolayer MoS2, the luminescence of the lowest-energy levels is linearly polarized and persists up to room temperature, meaning that it could be exploited in a variety of light-emitting applications.
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Affiliation(s)
- Andrés Granados Del Águila
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371
| | - Sheng Liu
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371
| | - T Thu Ha Do
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371
| | - Zhuangchai Lai
- Center for Programmable Materials, School of Materials Science and Engineering , Nanyang Technological University , Singapore , Singapore 639977
| | - Thu Ha Tran
- Center for Programmable Materials, School of Materials Science and Engineering , Nanyang Technological University , Singapore , Singapore 639977
| | - Sean Ryan Krupp
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371
| | - Zhi-Rui Gong
- College of Physics and Energy , Shenzhen University , Shenzhen 518060 , China
| | - Hua Zhang
- Center for Programmable Materials, School of Materials Science and Engineering , Nanyang Technological University , Singapore , Singapore 639977
- Department of Chemistry , City University of Hong Kong , Kowloon , Hong Kong , China
| | - Wang Yao
- Department of Physics , University of Hong Kong , Hong Kong , China
| | - Qihua Xiong
- Division of Physics and Applied Physics, School of Physical and Mathematical Sciences , Nanyang Technological University , Singapore 637371
- MajuLab , CNRS-UNS-NUS-NTU International Joint Research Unit , UMI 3654 , Singapore 639798
- NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering , Nanyang Technological University, Singapore 639798
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8
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Plechinger G, Nagler P, Arora A, Granados Del Águila A, Ballottin MV, Frank T, Steinleitner P, Gmitra M, Fabian J, Christianen PCM, Bratschitsch R, Schüller C, Korn T. Excitonic Valley Effects in Monolayer WS 2 under High Magnetic Fields. Nano Lett 2016; 16:7899-7904. [PMID: 27960453 DOI: 10.1021/acs.nanolett.6b04171] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Transition-metal dichalcogenides can be easily produced as atomically thin sheets, exhibiting the possibility to optically polarize and read out the valley pseudospin of extremely stable excitonic quasiparticles present in these 2D semiconductors. Here, we investigate a monolayer of tungsten disulfide in high magnetic fields up to 30 T via photoluminescence spectroscopy at low temperatures. The valley degeneracy is lifted for all optical features, particularly for excitons, singlet and triplet trions, for which we determine the g factor separately. While the observation of a diamagnetic shift of the exciton and trion resonances gives us insight into the real-space extension of these quasiparticles, magnetic field-induced valley polarization effects shed light onto the exciton and trion dispersion relations in reciprocal space. The field dependence of the trion valley polarizations is in line with the predicted trion splitting into singlet and triplet configurations.
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Affiliation(s)
- Gerd Plechinger
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Philipp Nagler
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Ashish Arora
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
| | - Andrés Granados Del Águila
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Mariana V Ballottin
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Tobias Frank
- Institut für Theoretische Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Philipp Steinleitner
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Martin Gmitra
- Institut für Theoretische Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Jaroslav Fabian
- Institut für Theoretische Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
| | - Rudolf Bratschitsch
- Institute of Physics and Center for Nanotechnology, University of Münster , 48149 Münster, Germany
| | - Christian Schüller
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg , D-93040 Regensburg, Germany
| | - Tobias Korn
- Institut für Experimentelle und Angewandte Physik, Universität Regensburg , D-93040 Regensburg, Germany
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9
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Schmidt R, Arora A, Plechinger G, Nagler P, Granados Del Águila A, Ballottin MV, Christianen PCM, Michaelis de Vasconcellos S, Schüller C, Korn T, Bratschitsch R. Magnetic-Field-Induced Rotation of Polarized Light Emission from Monolayer WS_{2}. Phys Rev Lett 2016; 117:077402. [PMID: 27563997 DOI: 10.1103/physrevlett.117.077402] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Indexed: 06/06/2023]
Abstract
We control the linear polarization of emission from the coherently emitting K^{+} and K^{-} valleys (valley coherence) in monolayer WS_{2} with an out-of-plane magnetic field of up to 25 T. The magnetic-field-induced valley Zeeman splitting causes a rotation of the emission polarization with respect to the excitation by up to 35° and reduces the polarization degree by up to 16%. We explain both of these phenomena with a model based on two noninteracting coherent two-level systems. We deduce that the coherent light emission from the valleys decays with a time constant of τ_{c}=260 fs.
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Affiliation(s)
- Robert Schmidt
- Institute of Physics and Center for Nanotechnology, University of Münster, 48149 Münster, Germany
| | - Ashish Arora
- Institute of Physics and Center for Nanotechnology, University of Münster, 48149 Münster, Germany
| | - Gerd Plechinger
- Department of Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Philipp Nagler
- Department of Physics, University of Regensburg, 93040 Regensburg, Germany
| | | | - Mariana V Ballottin
- High Field Magnet Laboratory (HFML-EMFL), Radboud University, 6525 ED Nijmegen, The Netherlands
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML-EMFL), Radboud University, 6525 ED Nijmegen, The Netherlands
| | | | - Christian Schüller
- Department of Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Tobias Korn
- Department of Physics, University of Regensburg, 93040 Regensburg, Germany
| | - Rudolf Bratschitsch
- Institute of Physics and Center for Nanotechnology, University of Münster, 48149 Münster, Germany
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10
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Granados Del Águila A, Groeneveld E, Maan JC, de Mello Donegá C, Christianen PCM. Effect of Electron-Hole Overlap and Exchange Interaction on Exciton Radiative Lifetimes of CdTe/CdSe Heteronanocrystals. ACS Nano 2016; 10:4102-10. [PMID: 26982795 DOI: 10.1021/acsnano.5b07158] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Wave function engineering has become a powerful tool to tailor the optical properties of semiconductor colloidal nanocrystals. Core-shell systems allow to design the spatial extent of the electron (e) and hole (h) wave functions in the conduction- and valence bands, respectively. However, tuning the overlap between the e- and h-wave functions not only affects the oscillator strength of the coupled e-h pairs (excitons) that are responsible for the light emission, but also modifies the e-h exchange interaction, leading to an altered excitonic energy spectrum. Here, we present exciton lifetime measurements in a strong magnetic field to determine the strength of the e-h exchange interaction, independently of the e-h overlap that is deduced from lifetime measurements at room temperature. We use a set of CdTe/CdSe core/shell heteronanocrystals in which the electron-hole separation is systematically varied. We are able to unravel the separate effects of e-h overlap and e-h exchange on the exciton lifetimes, and we present a simple model that fully describes the recombination lifetimes of heteronanostructures (HNCs) as a function of core volume, shell volume, temperature, and magnetic fields.
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Affiliation(s)
- Andrés Granados Del Águila
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
- Institute for Molecules and Materials, Radboud University , 6525 AJ Nijmegen, The Netherlands
| | - Esther Groeneveld
- Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science , Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Jan C Maan
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
- Institute for Molecules and Materials, Radboud University , 6525 AJ Nijmegen, The Netherlands
| | - Celso de Mello Donegá
- Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science , Princetonplein 1, 3584 CC Utrecht, The Netherlands
| | - Peter C M Christianen
- High Field Magnet Laboratory (HFML-EMFL), Radboud University , 6525 ED Nijmegen, The Netherlands
- Institute for Molecules and Materials, Radboud University , 6525 AJ Nijmegen, The Netherlands
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11
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Granados Del Águila A, Jha B, Pietra F, Groeneveld E, de Mello Donegá C, Maan JC, Vanmaekelbergh D, Christianen PCM. Observation of the full exciton and phonon fine structure in CdSe/CdS dot-in-rod heteronanocrystals. ACS Nano 2014; 8:5921-31. [PMID: 24861569 DOI: 10.1021/nn501026t] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Light emission of semiconductor nanocrystals is a complex process, depending on many factors, among which are the quantum mechanical size confinement of excitons (coupled electron-hole pairs) and the influence of confined phonon modes and the nanocrystal surface. Despite years of research, the nature of nanocrystal emission at low temperatures is still under debate. Here we unravel the different optical recombination pathways of CdSe/CdS dot-in-rod systems that show an unprecedented number of narrow emission lines upon resonant laser excitation. By using self-assembled, vertically aligned rods and application of crystallographically oriented high magnetic fields, the origin of all these peaks is established. We observe a clear signature of an acoustic-phonon assisted transition, separated from the zero-phonon emission and optical-phonon replica, proving that nanocrystal light emission results from an intricate interplay between bright (optically allowed) and dark (optically forbidden) exciton states, coupled to both acoustic and optical phonon modes.
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Affiliation(s)
- Andrés Granados Del Águila
- High Field Magnet Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen , Toernooiveld 7, 6525 ED Nijmegen, The Netherlands
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