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Observation of ultralong valley lifetime in WSe2/MoS2heterostructures

  • Author(s): Kim, J
  • Jin, C
  • Chen, B
  • Cai, H
  • Zhao, T
  • Lee, P
  • Kahn, S
  • Watanabe, K
  • Taniguchi, T
  • Tongay, S
  • Crommie, MF
  • Wang, F
  • et al.
Abstract

© Copyright 2017 The Authors, some rights reserved. The valley degree of freedom in two-dimensional (2D) crystals recently emerged as a novel information carrier in addition to spin and charge. The intrinsic valley lifetime in 2D transition metal dichalcogenides (TMD) is expected to be markedly long due to the unique spin-valley locking behavior, where the intervalley scattering of the electron simultaneously requires a large momentum transfer to the opposite valley and a flip of the electron spin. However, the experimentally observed valley lifetime in 2D TMDs has been limited to tens of nanoseconds thus far. We report efficient generation of microsecond-long-lived valley polarization in WSe2/MoS2heterostructures by exploiting the ultrafast charge transfer processes in the heterostructure that efficiently creates resident holes in the WSe2layer. These valley-polarized holes exhibit near-unity valley polarization and ultralong valley lifetime: We observe a valley-polarized hole population lifetime of more than 1 ms and a valley depolarization lifetime (that is, intervalley scattering lifetime) of more than 40 ms at 10 K. The near-perfect generation of valley-polarized holes in TMD heterostructures, combined with ultralong valley lifetime, which is orders of magnitude longer than previous results, opens up new opportunities for novel valleytronics and spintronics applications.

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