Evidence of Spin-Valley Coupling in Dirac Material BaMnBi2 Probed by Quantum Hall Effect and Nonlinear Hall Effect

TL;DR

This study provides experimental evidence of spin valley coupling in bulk BaMnBi2, revealing quantum Hall and nonlinear Hall effects that demonstrate unique valley-locked electronic states with potential for valleytronic applications.

Contribution

It reports the first observation of spin valley locked states in a bulk material, expanding valleytronics beyond monolayer transition metal dichalcogenides.

Findings

Observation of stacked quantum Hall effect in BaMnBi2

Detection of nonlinear Hall effect indicating valley-contrasted Berry curvature

Identification of spin valley degeneracy of four in BaMnBi2

Abstract

Valleytronics is a rapidly advancing field that explores the use of the valley degree of freedom in electronic systems to encode and process information. It relies on electronic states with spin valley locking, first predicted and observed in monolayer transition metal dichalcogenides such as MoS2. However, very few bulk materials have been reported to host spin valley locked electronic states. In this work, we present experimental evidence for a predicted, unique spin valley locked electronic state generated by Bi zigzag chains in the layered compound BaMnBi2. We observe remarkable quantum transport properties in this material, including a stacked quantum Hall effect (QHE) and a nonlinear Hall effect (NLHE). From the analysis of the QHE, we identify a spin valley degeneracy of four, while the NLHE provides supporting evidence for the anticipated valley contrasted Berry curvature, a typical signature of a spin valley locked state. This spin valley locked state contrasts with that observed in the sister compound BaMnSb2, where the degeneracy is two. This difference arises from significant variations in their orthorhombic crystal structures and spin orbit coupling. These findings establish a new platform for exploring coupled spin valley physics in bulk materials and highlight its potential for valleytronic device applications.