Ultrafast non-excitonic valley Hall effect in MoS2/WTe2 heterobilayers

Abstract

<jats:title>Abstract</jats:title><jats:p>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<jats:sub>2</jats:sub>/WTe<jats:sub>2</jats:sub> 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<jats:sub>2</jats:sub> 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<jats:sup>3</jats:sup> cm<jats:sup>2</jats:sup>/Vs, which is orders of magnitude larger than previous reports.</jats:p>