Stacked Quantum Hall Effect in BaMnBi₂

Quantum Hall effect (QHE) in three dimensional materials have recently attracted intense interest. In this presentation, we report a stacked QHE in the layered Dirac material BaMnBi₂. This compound possesses a non-centrosymmetric orthorhombic structure (Imm2) with alternating stack of 2D Bi zig-zag chain layers and Ba-MnBi₄-Ba insulating slabs [1]. The non-centrosymmetric orthorhombic structure and strong spin-orbit coupling give rise to quasi-2D massive Dirac fermions with spin-valley locking. Recently, the bulk QHE has been experimentally verified in BaMnSb₂ to come from spin-valley locked Dirac fermions [2]. Recent studies suggest that BaMnBi₂ exhibits a spin-valley locked state differing from that in BaMnSb₂ due to its weaker lattice distortion. Such a spin-valley locked state is also expected to yield a stacked QHE, but is not verified experimentally yet. From our magneto-transport measurements on BaMnBi₂ bulk single crystals under high fields (up to 35T), we found evidence of stacked QHE. We observed not only two quantized Hall resistivity plateaus with filing factors of 1/2 and 3/2, but also the Zeeman splitting of the zeroth Landau level. These results deepen our understanding of the bulk spin-valley locked state in BaMnBi₂.