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Title: Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2

The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin–valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments PL timescales are necessarily constrained by short-lived (3–100 ps) electron–hole recombination9, 10. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin–valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns at 5 K (2-3 orders of magnitude longer than typical exciton recombination times). In contrast with conventional III–V or II–VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin–valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin–orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [3] ;  [3] ;  [1]
  1. National High Magnetic Field Lab., Los Alamos, NM (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Rice Univ., Houston, TX (United States)
Publication Date:
OSTI Identifier:
1235921
Report Number(s):
LA-UR--15-22447
Journal ID: ISSN 1745-2473; nphys3419
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Nature Physics
Additional Journal Information:
Journal Volume: 11; Journal Issue: 10; Journal ID: ISSN 1745-2473
Publisher:
Nature Publishing Group (NPG)
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY spintronics; two-dimensional materials