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

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.