Evidence of spin-valley coupling in Dirac material BaMnBi₂probed by quantum Hall effect and nonlinear Hall effect

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 like 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 the Bi zig-zag chains in the layered compound BaMnBi2. We observed remarkable quantum transport properties in this material, including stacked quantum Hall effect (QHE) and nonlinear Hall effect (NLHE). From the analysis of the QHE, we identified a spin-valley degeneracy of 4, 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 2. This difference arises from significant variations in their orthorhombic structures and spin-orbital coupling. These findings not only set up a new platform for exploring coupled spin-valley physics in bulk materials but also underscores its potential for valleytronic device applications.