Observation of Ultralong Valley Lifetime in WSe2/MoS2 Heterostructures

TL;DR

This paper reports the observation of ultralong valley lifetimes exceeding 40 microseconds in WSe2/MoS2 heterostructures, achieved through ultrafast charge transfer, significantly surpassing previous results and advancing valleytronics potential.

Contribution

It demonstrates for the first time microsecond-long valley polarization and ultralong valley lifetime in TMD heterostructures, enabled by ultrafast charge transfer processes.

Findings

Valley polarization lifetime exceeds 1 microsecond.

Valley depolarization lifetime over 40 microseconds at 10 K.

Ultrafast charge transfer creates highly polarized holes.

Abstract

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 dichalcoginides (TMD) is expected to be remarkably long due to the unique spin-valley locking behavior, where the inter-valley scattering of electron requires simultaneously a large momentum transfer to the opposite valley and a flip of the electron spin. The experimentally observed valley lifetime in 2D TMDs, however, has been limited to tens of nanoseconds so far. Here we report efficient generation of microsecond-long lived valley polarization in WSe2/MoS2 heterostructures by exploiting the ultrafast charge transfer processes in the heterostructure that efficiently creates resident holes in the WSe2 layer. These valley-polarized holes exhibit near unity valley polarization and ultralong valley lifetime: we observe a valley-polarized hole population lifetime of over 1 us, and a valley depolarization lifetime (i.e. inter-valley scattering lifetime) over 40 us at 10 Kelvin. The near-perfect generation of valley-polarized holes in TMD heterostructures with ultralong valley lifetime, orders of magnitude longer than previous results, opens up new opportunities for novel valleytronics and spintronics applications.