Bulk quantum Hall effect of spin-valley coupled Dirac fermions in the polar antiferromagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">BaMnSb</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Hideaki Sakai, H. Fujimura, Shunsuke Sakuragi, Masayuki Ochi, Ryosuke Kurihara, Atsushi Miyake, Masashi Tokunaga, Tatsuhiro Kojima, Daisuke Hashizume, Takayuki Muro, Kenta Kuroda, Takeshi Kondo, Takanori Kida, Masayuki Hagiwara, K. Kuroki, Masaki Kondo, K. Tsuruda, H. Murakawa, Noriaki Hanasaki
Abstract
Unconventional features of relativistic Dirac/Weyl quasiparticles in topological materials are most evidently manifested in the two-dimensional quantum Hall effect (QHE), whose variety is further enriched by their spin and/or valley polarization. Although its extension to three dimensions has been long sought and inspired theoretical proposals, material candidates have been lacking. Here, we have discovered valley-contrasting spin-polarized Dirac fermions in a multilayer form in the bulk antiferromagnet ${\mathrm{BaMnSb}}_{2}$, where out-of-plane Zeeman-type spin splitting is induced by in-plane inversion symmetry breaking and spin-orbit coupling in the distorted Sb square net. Furthermore, we have observed well-defined quantized Hall plateaus together with vanishing interlayer conductivity at low temperatures as a hallmark of the half-integer QHE in a bulk form. The Hall conductance of each layer is found to be nearly quantized to $2(N+1/2){e}^{2}/h$, with $N$ being the Landau index, which is consistent with two spin-polarized Dirac valleys protected by the strong spin-valley coupling.