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Title: Nonlinear optical selection rule based on valley-exciton locking in monolayer ws 2

Optical selection rules fundamentally determine the optical transitions between energy states in a variety of physical systems, from hydrogen atoms to bulk crystals such as gallium arsenide. These rules are important for optoelectronic applications such as lasers, energy-dispersive X-ray spectroscopy, and quantum computation. Recently, single-layer transition metal dichalcogenides have been found to exhibit valleys in momentum space with nontrivial Berry curvature and excitons with large binding energy. However, there has been little study of how the unique valley degree of freedom combined with the strong excitonic effect influences the nonlinear optical excitation. Here in this paper, we report the discovery of nonlinear optical selection rules in monolayer WS 2, an important candidate for visible 2D optoelectronics because of its high quantum yield and large direct bandgap. We experimentally demonstrated this principle for second-harmonic generation and two-photon luminescence (TPL). Moreover, the circularly polarized TPL and the study of its dynamics evince a sub-ps interexciton relaxation (2p → 1s). The discovery of this new optical selection rule in a valleytronic 2D system not only considerably enhances knowledge in this area but also establishes a foundation for the control of optical transitions that will be crucial for valley optoelectronic device applications such asmore » 2D valley-polarized THz sources with 2p-1s transitions, optical switches, and coherent control for quantum computing.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [2] ;  [3]
  1. Univ. of California, Berkeley, CA (United States). NSF Nanoscale Science and Engineering Center (NSEC)
  2. Univ. of California, Berkeley, CA (United States). NSF Nanoscale Science and Engineering Center (NSEC); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Material Sciences Division
  3. Univ. of California, Berkeley, CA (United States). NSF Nanoscale Science and Engineering Center (NSEC); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Material Sciences Division; King Abdulaziz Univ., Jeddah (Saudi Arabia). Dept. of Physics
Publication Date:
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
Light, Science & Applications
Additional Journal Information:
Journal Volume: 4; Journal Issue: 12; Journal ID: ISSN 2047-7538
Publisher:
Nature Publishing Group
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Nonlinear optics; Optical materials and structures; Nonlinear optical selection rule; 2D materials; 2p–1s exciton relaxation; Valley exciton
OSTI Identifier:
1415947