Mazin Igor I, Koepernik Klaus, Johannes Michelle D, González-Hernández Rafael, Šmejkal Libor
Department of Physics and Astronomy, George Mason University, Fairfax, VA 22030;
Center for Quantum Science and Engineering, George Mason University, Fairfax, VA 22030.
Proc Natl Acad Sci U S A. 2021 Oct 19;118(42). doi: 10.1073/pnas.2108924118.
It is commonly believed that the energy bands of typical collinear antiferromagnets (AFs), which have zero net magnetization, are Kramers spin-degenerate. Kramers nondegeneracy is usually associated with a global time-reversal symmetry breaking (e.g., via ferromagnetism) or with a combination of spin-orbit interaction and broken spatial inversion symmetry. Recently, another type of spin splitting was demonstrated to emerge in some collinear magnets that are fully spin compensated by symmetry, nonrelativistic, and not even necessarily noncentrosymmetric. These materials feature nonzero spin density staggered in real space as seen in traditional AFs but also spin splitting in momentum space, generally seen only in ferromagnets. This results in a combination of materials characteristics typical of both ferromagnets and AFs. Here, we discuss this recently discovered class with application to a well-known semiconductor, FeSb, and predict that with certain alloying, it becomes magnetic and metallic and features the aforementioned magnetic dualism. The calculated energy bands split antisymmetrically with respect to spin-degenerate nodal surfaces rather than nodal points, as in the case of spin-orbit splitting. The combination of a large (0.2-eV) spin splitting, compensated net magnetization with metallic ground state, and a specific magnetic easy axis generates a large anomalous Hall conductivity (∼150 S/cm) and a sizable magnetooptical Kerr effect, all deemed to be hallmarks of nonzero net magnetization. We identify a large contribution to the anomalous response originating from the spin-orbit interaction gapped anti-Kramers nodal surfaces, a mechanism distinct from the nodal lines and Weyl points in ferromagnets.
人们普遍认为，典型的共线反铁磁体（AFs）的能带具有零净磁化强度，是克莱默斯自旋简并的。克莱默斯非简并通常与全局时间反演对称性破缺（例如，通过铁磁性）或自旋轨道相互作用与空间反演对称性破缺的组合相关。最近，在一些共线磁体中发现了另一种类型的自旋分裂，这些磁体在对称性、非相对论性方面是完全自旋补偿的，甚至不一定是非中心对称的。这些材料在实空间中具有如传统反铁磁体中所见的非零自旋密度交错，但在动量空间中也有自旋分裂，这通常仅在铁磁体中出现。这导致了铁磁体和反铁磁体典型材料特性的结合。在这里，我们讨论这种最近发现的类型，并将其应用于一种著名的半导体FeSb，并预测通过特定的合金化，它会变成磁性和金属性的，并具有上述磁二元性。计算得到的能带相对于自旋简并的节面而不是节点进行反对称分裂，这与自旋轨道分裂的情况不同。大的（0.2电子伏特）自旋分裂、具有金属基态的补偿净磁化强度以及特定的磁易轴的组合产生了大的反常霍尔电导率（约150 S/cm）和可观的磁光克尔效应，所有这些都被认为是非零净磁化强度的标志。我们确定，反常响应的很大一部分源自自旋轨道相互作用带隙的反克莱默斯节面，这是一种与铁磁体中的节线和外尔点不同的机制。
