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Title: Magnetic brightening and control of dark excitons in monolayer WSe 2

Monolayer transition metal dichalcogenide crystals, as direct-gap materials with strong light–matter interactions, have attracted much recent attention. Because of their spin-polarized valence bands and a predicted spin splitting at the conduction band edges, the lowest-lying excitons in WX 2 (X = S, Se) are expected to be spin-forbidden and optically dark. To date, however, there has been no direct experimental probe of these dark excitons. Here, we show how an in-plane magnetic field can brighten the dark excitons in monolayer WSe2 and permit their properties to be observed experimentally. Precise energy levels for both the neutral and charged dark excitons are obtained and compared with ab initio calculations using the GW-BSE approach. As a result of their spin configuration, the brightened dark excitons exhibit much-increased emission and valley lifetimes. Furthermore, these studies directly probe the excitonic spin manifold and reveal the fine spin-splitting at the conduction band edges.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [3] ;  [6] ;  [5] ;  [4] ;  [6] ;  [2] ;  [7]
  1. Columbia Univ., New York, NY (United States); Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
  2. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. National High Magnetic Field Lab., Tallahassee, FL (United States); Florida State Univ., Tallahassee, FL (United States)
  4. The Pennsylvania State Univ., University Park, PA (United States)
  5. Columbia Univ., New York, NY (United States)
  6. National High Magnetic Field Lab., Tallahassee, FL (United States)
  7. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; GBMF4545; FA9550-14-1-0040; AC02-05CH11231; DMR-1508412; DMR-1420634; DMR-1157490
Type:
Accepted Manuscript
Journal Name:
Nature Nanotechnology
Additional Journal Information:
Journal Volume: 12; Journal Issue: 9; Journal ID: ISSN 1748-3387
Publisher:
Nature Publishing Group
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); Betty and Gordon Moore Foundation
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1367175
Alternate Identifier(s):
OSTI ID: 1458504

Zhang, Xiao -Xiao, Cao, Ting, Lu, Zhengguang, Lin, Yu -Chuan, Zhang, Fan, Wang, Ying, Li, Zhiqiang, Hone, James C., Robinson, Joshua A., Smirnov, Dmitry, Louie, Steven G., and Heinz, Tony F.. Magnetic brightening and control of dark excitons in monolayer WSe2. United States: N. p., Web. doi:10.1038/NNANO.2017.105.
Zhang, Xiao -Xiao, Cao, Ting, Lu, Zhengguang, Lin, Yu -Chuan, Zhang, Fan, Wang, Ying, Li, Zhiqiang, Hone, James C., Robinson, Joshua A., Smirnov, Dmitry, Louie, Steven G., & Heinz, Tony F.. Magnetic brightening and control of dark excitons in monolayer WSe2. United States. doi:10.1038/NNANO.2017.105.
Zhang, Xiao -Xiao, Cao, Ting, Lu, Zhengguang, Lin, Yu -Chuan, Zhang, Fan, Wang, Ying, Li, Zhiqiang, Hone, James C., Robinson, Joshua A., Smirnov, Dmitry, Louie, Steven G., and Heinz, Tony F.. 2017. "Magnetic brightening and control of dark excitons in monolayer WSe2". United States. doi:10.1038/NNANO.2017.105. https://www.osti.gov/servlets/purl/1367175.
@article{osti_1367175,
title = {Magnetic brightening and control of dark excitons in monolayer WSe2},
author = {Zhang, Xiao -Xiao and Cao, Ting and Lu, Zhengguang and Lin, Yu -Chuan and Zhang, Fan and Wang, Ying and Li, Zhiqiang and Hone, James C. and Robinson, Joshua A. and Smirnov, Dmitry and Louie, Steven G. and Heinz, Tony F.},
abstractNote = {Monolayer transition metal dichalcogenide crystals, as direct-gap materials with strong light–matter interactions, have attracted much recent attention. Because of their spin-polarized valence bands and a predicted spin splitting at the conduction band edges, the lowest-lying excitons in WX2 (X = S, Se) are expected to be spin-forbidden and optically dark. To date, however, there has been no direct experimental probe of these dark excitons. Here, we show how an in-plane magnetic field can brighten the dark excitons in monolayer WSe2 and permit their properties to be observed experimentally. Precise energy levels for both the neutral and charged dark excitons are obtained and compared with ab initio calculations using the GW-BSE approach. As a result of their spin configuration, the brightened dark excitons exhibit much-increased emission and valley lifetimes. Furthermore, these studies directly probe the excitonic spin manifold and reveal the fine spin-splitting at the conduction band edges.},
doi = {10.1038/NNANO.2017.105},
journal = {Nature Nanotechnology},
number = 9,
volume = 12,
place = {United States},
year = {2017},
month = {6}
}

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