Observation of Valley Zeeman and Quantum Hall Effects at Q Valley of Few-Layer Transition Metal Disulfides

TL;DR

This paper reports the observation of valley Zeeman and quantum Hall effects in few-layer transition metal disulfides, revealing spin-valley coupling and high mobility transport phenomena in these materials.

Contribution

It presents the first transport characterization of Q valley electrons and the quantum Hall effect in TMDCs, highlighting the role of layer parity in spin and valley effects.

Findings

Observation of valley Zeeman effect in odd-layer TMDs

Observation of spin Zeeman effect in even-layer TMDs

High field-effect mobilities (~16,000 and ~10,500 cm2V-1s-1) at cryogenic temperatures

Abstract

In few-layer (FL) transition metal dichalcogenides (TMDC), the conduction bands along the Gamma-K directions shift downward energetically in the presence of interlayer interactions, forming six Q valleys related by three-fold rotational symmetry and time reversal symmetry. In even-layers the extra inversion symmetry requires all states to be Kramers degenerate, whereas in odd-layers the intrinsic inversion asymmetry dictates the Q valleys to be spin-valley coupled. In this Letter, we report the transport characterization of prominent Shubnikov-de Hass (SdH) oscillations for the Q valley electrons in FL transition metal disulfide (TMDs), as well as the first quantum Hall effect (QHE) in TMDCs. Our devices exhibit ultrahigh field-effect mobilities (~16,000 cm2V-1s-1 for FL WS2 and ~10,500 cm2V-1s-1 for FL MoS2) at cryogenic temperatures. Universally in the SdH oscillations, we observe a valley Zeeman effect in all odd-layer TMD devices and a spin Zeeman effect in all even-layer TMD devices.