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Title: Negative electronic compressibility and tunable spin splitting in WSe 2

Abstract

We report that tunable bandgaps, extraordinarily large exciton-binding energies, strong light-matter coupling and a locking of the electron spin with layer and valley pseudospins have established transition-metal dichalcogenides (TMDs) as a unique class of two-dimensional (2D) semiconductors with wide-ranging practical applications. Using angle-resolved photoemission (ARPES), we show here that doping electrons at the surface of the prototypical strong spin-orbit TMD WSe 2, akin to applying a gate voltage in a transistor-type device, induces a counterintuitive lowering of the surface chemical potential concomitant with the formation of a multivalley 2D electron gas (2DEG). These measurements provide a direct spectroscopic signature of negative electronic compressibility (NEC), a result of electron-electron interactions, which we find persists to carrier densities approximately three orders of magnitude higher than in typical semiconductor 2DEGs that exhibit this effect. An accompanying tunable spin splitting of the valence bands further reveals a complex interplay between single-particle band-structure evolution and many-body interactions in electrostatically doped TMDs. Lastly, understanding and exploiting this will open up new opportunities for advanced electronic and quantum-logic devices.

Authors:
 [1];  [2];  [3];  [4];  [5];  [2];  [6];  [6]; ORCiD logo [7];  [5];  [4];  [8]; ORCiD logo [3]
  1. Univ. of St. Andrews, Scotland (United Kingdom); Diamond Light Source, Harwell Campus, Didcot (United Kingdom)
  2. Suranaree University of Technology, Nakhon Ratchasima (Thailand)
  3. Univ. of St. Andrews, Scotland (United Kingdom)
  4. Tokyo Institute of Technology, Kanagawa (Japan)
  5. Univ. of Tokyo (Japan); Max Planck Institute for Solid State Research, Stuttgart (Germany)
  6. Diamond Light Source, Harwell Campus, Didcot (United Kingdom)
  7. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  8. Univ. of Tokyo (Japan); RIKEN Center for Emergent Matter Science (CEMS), Wako (Japan)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1530213
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Nature Nanotechnology
Additional Journal Information:
Journal Volume: 10; Journal Issue: 12; Journal ID: ISSN 1748-3387
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Riley, J. M., Meevasana, W., Bawden, L., Asakawa, M., Takayama, T., Eknapakul, T., Kim, T. K., Hoesch, M., Mo, S. -K., Takagi, H., Sasagawa, T., Bahramy, M. S., and King, P. D. C. Negative electronic compressibility and tunable spin splitting in WSe2. United States: N. p., 2015. Web. doi:10.1038/nnano.2015.217.
Riley, J. M., Meevasana, W., Bawden, L., Asakawa, M., Takayama, T., Eknapakul, T., Kim, T. K., Hoesch, M., Mo, S. -K., Takagi, H., Sasagawa, T., Bahramy, M. S., & King, P. D. C. Negative electronic compressibility and tunable spin splitting in WSe2. United States. doi:10.1038/nnano.2015.217.
Riley, J. M., Meevasana, W., Bawden, L., Asakawa, M., Takayama, T., Eknapakul, T., Kim, T. K., Hoesch, M., Mo, S. -K., Takagi, H., Sasagawa, T., Bahramy, M. S., and King, P. D. C. Mon . "Negative electronic compressibility and tunable spin splitting in WSe2". United States. doi:10.1038/nnano.2015.217. https://www.osti.gov/servlets/purl/1530213.
@article{osti_1530213,
title = {Negative electronic compressibility and tunable spin splitting in WSe2},
author = {Riley, J. M. and Meevasana, W. and Bawden, L. and Asakawa, M. and Takayama, T. and Eknapakul, T. and Kim, T. K. and Hoesch, M. and Mo, S. -K. and Takagi, H. and Sasagawa, T. and Bahramy, M. S. and King, P. D. C.},
abstractNote = {We report that tunable bandgaps, extraordinarily large exciton-binding energies, strong light-matter coupling and a locking of the electron spin with layer and valley pseudospins have established transition-metal dichalcogenides (TMDs) as a unique class of two-dimensional (2D) semiconductors with wide-ranging practical applications. Using angle-resolved photoemission (ARPES), we show here that doping electrons at the surface of the prototypical strong spin-orbit TMD WSe2, akin to applying a gate voltage in a transistor-type device, induces a counterintuitive lowering of the surface chemical potential concomitant with the formation of a multivalley 2D electron gas (2DEG). These measurements provide a direct spectroscopic signature of negative electronic compressibility (NEC), a result of electron-electron interactions, which we find persists to carrier densities approximately three orders of magnitude higher than in typical semiconductor 2DEGs that exhibit this effect. An accompanying tunable spin splitting of the valence bands further reveals a complex interplay between single-particle band-structure evolution and many-body interactions in electrostatically doped TMDs. Lastly, understanding and exploiting this will open up new opportunities for advanced electronic and quantum-logic devices.},
doi = {10.1038/nnano.2015.217},
journal = {Nature Nanotechnology},
number = 12,
volume = 10,
place = {United States},
year = {2015},
month = {9}
}

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