Ultrafast non-excitonic valley Hall effect in MoS2/WTe2 heterobilayers
Jekwan Lee, Wonhyeok Heo, Myungjun Cha, Kenji Watanabe, Takashi Taniguchi, Jehyun Kim, Soonyoung Cha, Dohun Kim, Moon‐Ho Jo, Hyunyong Choi
Abstract
Abstract 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 MoS 2 /WTe 2 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 MoS 2 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 × 10 3 cm 2 /Vs, which is orders of magnitude larger than previous reports.