In non-centrosymmetric metals, spin-orbit coupling induces momentum-dependent spin polarization at the Fermi surfaces. This is exemplified by the valley-contrasting spin polarization in monolayer transition metal dichalcogenides with in-plane inversion asymmetry. However, the valley configuration of massive Dirac fermions in transition metal dichalcogenides is fixed by the graphene-like structure, which limits the variety of spin-valley coupling. Here, we show that the layered polar metal BaMnX₂ (X = Bi, Sb) hosts tunable spin-valley-coupled Dirac fermions, which originate from the distorted X square net with in-plane lattice polarization. We found that BaMnBi₂ has approximately one-tenth the lattice distortion of BaMnSb₂, from which a different configuration of spin-polarized Dirac valleys is theoretically predicted. This was experimentally observed as a clear difference in the Shubnikov-de Haas oscillation at high fields between the two materials. The chemically tunable spin-valley coupling in BaMnX₂ makes it a promising material for various spin-valleytronic devices.

在非中心对称金属中，自旋轨道耦合在费米表面上引起动量依赖的自旋极化。这可以通过具有面内反型不对称性的单层过渡金属二卤化物中的谷底自旋极化来举例说明。但是，过渡金属二卤化物中大量狄拉克费米子的谷底构型被石墨烯状结构所固定，这限制了自旋谷耦合的多样性。在这里，我们显示出层状极性金属BaMn X ₂（X  = Bi，Sb）拥有可调谐的自旋谷耦合Dirac费米子，它源自具有面内晶格极化的扭曲X平方网。我们发现BaMnBi ₂具有约十分之一的BaMnSb晶格畸变_参照图2，从理论上预测自旋极化的狄拉克谷的不同构型。通过实验观察到，这是两种材料在高场的Shubnikov-de Haas振荡中的明显差异。BaMn X _2中的化学可调自旋谷耦合使得它成为各种自旋谷电子器件的有前途的材料。