Electrical control of the valley Hall effect in bilayer MoS2 transistors

TL;DR

This paper demonstrates electrical control of the valley Hall effect in bilayer MoS2 transistors by breaking inversion symmetry with a gate electric field, enabling tunable valley polarization for valleytronics applications.

Contribution

It shows how to electrically tune the valley Hall effect in bilayer MoS2, overcoming the limitations of monolayer materials for valley-based electronic devices.

Findings

Gate electric field breaks inversion symmetry in bilayer MoS2.

Valley polarization can be imaged and is gate-dependent.

Valley Hall conductivity is consistent with symmetry-dependent Berry curvature.

Abstract

The valley degree of freedom of electrons in solids has been proposed as a new type of information carriers beyond the electronic charge and spin. Recent experimental demonstrations of the optical orientation of the valley polarization and generation of the valley current through the valley Hall effect in monolayer MoS2 have shown the potential of two-dimensional semiconductor transition metal dichalcogenides for valley based electronic and optoelectronic applications. The valley Hall conductivity in monolayer MoS2, a non-centrosymmetric crystal, however, cannot be easily tuned, presenting a challenge for valley-based applications. Here we report the control of the valley Hall effect in bilayer MoS2 transistors through a gate. The inversion symmetry present in bilayer MoS2 was broken by the gate applied electric field perpendicular to the plane. The valley polarization near the edges of the device channels induced by the longitudinal electrical current was imaged by use of Kerr rotation microscopy. The polarization is out-of-plane, has opposite sign for the two edges, and is strongly dependent on the gate voltage. The observation is consistent with the symmetry dependent Berry curvature and valley Hall conductivity in bilayer MoS2. Our results are another step towards information processing based on the valley degree of freedom.