The valley Hall effect (VHE) in two-dimensional (2D) van der Waals (vdW) crystals is a promising approach to study the valley pseudospin. Most experiments so far have used bound electron-hole pairs (excitons) through local photoexcitation. However, the valley depolarization of such excitons is fast, so that several challenges remain to be resolved. We address this issue by exploiting a unipolar VHE using a heterobilayer made of monolayer MoS2/WTe2 to exhibit a long valley-polarized lifetime due to the absence of electron-hole exchange interaction. The unipolar VHE is manifested by reduced photoluminescence at the MoS2 A exciton energy. Furthermore, we provide quantitative information on the time-dependent valley Hall dynamics by performing the spatially-resolved ultrafast Kerr-rotation microscopy; we find that the valley-polarized electrons persist for more than 4 nanoseconds and the valley Hall mobility exceeds 4.49 × 103 cm2/Vs, which is orders of magnitude larger than previous reports.
Bibliographical noteFunding Information:
J.L., W.H., M.C., and H.C. were supported by the National Research Foundation of Korea (NRF) through the government of Korea (MSIP) (Grant NRF-2018R1A2A1A05079060, NRF-2020M3F3A2A03082472), Creative Materials Discovery Program (Grant 2017M3D1A1040828), Scalable Quantum Computer Technology Platform Center (Grant 2019R1A5A1027055), and the Institute for Basic Science (IBS), Korea under Project code IBS-R014-G1-2018-A1. Part of this study has been performed using facilities at IBS Center for Correlated Electron Systems, Seoul National University.
© 2021, The Author(s).
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- Physics and Astronomy(all)