Most of solid-state spin physics arising from spin–orbit coupling, from fundamental phenomena to industrial applications, relies on symmetry-protected degeneracies. So does the Zeeman spin–orbit coupling, expected to manifest itself in a wide range of antiferromagnetic conductors. Yet, experimental proof of this phenomenon has been lacking. Here we demonstrate that the Néel state of the layered organic superconductor κ-(BETS)₂FeBr₄ shows no spin modulation of the Shubnikov–de Haas oscillations, contrary to its paramagnetic state. This is unambiguous evidence for the spin degeneracy of Landau levels, a direct manifestation of the Zeeman spin–orbit coupling. Likewise, we show that spin modulation is absent in electron-doped Nd_1.85Ce_0.15CuO₄, which evidences the presence of Néel order in this cuprate superconductor even at optimal doping. Obtained on two very different materials, our results demonstrate the generic character of the Zeeman spin–orbit coupling.

大多数自旋轨道耦合产生的固态自旋物理学，从基本现象到工业应用，都依赖于对称保护的简并性。Zeeman自旋轨道耦合也是如此，有望在广泛的反铁磁导体中表现出来。然而，缺乏对此现象的实验证明。在这里，我们证明了层状有机超导体κ-（BETS）₂ FeBr ₄的Néel态与其顺磁态相反，没有显示Shubnikov-de Haas振荡的自旋调制。这是Landau能级自旋简并性的明确证据，这是Zeeman自旋-轨道耦合的直接体现。同样，我们表明在电子掺杂的Nd _1.85 Ce中不存在自旋调制_0.15 CuO ₄，即使在最佳掺杂下，也证明该铜酸盐超导体中存在Néel有序。在两种截然不同的材料上获得的结果证明了塞曼自旋轨道耦合的一般特性。