发表机构
Hong Kong University of Science and Technology（香港科技大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究发现非手性不可接受反铁磁体中存在赫施节点线，其会产生大量无质量狄拉克锥，且这类材料的非线性反常霍尔效应最低非零阶为三阶，第一性原理计算在MnTe等材料中证实了该预测。
AI 中文摘要
近期，一类新型反铁磁体中的外尔半金属——赫施外尔半金属被发现，这类材料具有不可接受的手性磁点群对称性（不可接受磁点群与铁磁序不兼容），并拥有独特的表面费米弧。在赫施外尔半金属中，外尔点被固定在布里渊区具有二维不可约核心表示的高对称动量处，由于外尔点被固定，其无法像传统外尔半金属中那样产生或合并相反拓扑电荷的外尔点以实现产生与湮灭。本研究表明，当镜面或旋转反演对称性恢复，使点群变为非手性时，会出现连接相反拓扑电荷外尔点的长双重简并线，我们将这类线命名为赫施节点线（HNLs），其宿主材料则称为赫施节点线反铁磁体。HNL会在布里渊区中与HNL相交的平面上产生大量二维无质量狄拉克锥；此外，大部分HNL反铁磁体具有特殊性质，即非线性反常霍尔效应的最低非零阶始于三阶。对MnTe、CrSb、Mn₃GaN等代表性共线与非共线反铁磁体的第一性原理计算，证实了HNL的存在预测。当应变打破不可接受对称性时，HNL的双重简并会被解除，相关无质量狄拉克锥会产生能隙，为在反铁磁晶体中实现可观的反常霍尔效应提供了途径。我们得出结论：所有无宇称-时间对称性的不可接受反铁磁体均为拓扑材料，它们要么是赫施外尔反铁磁体，要么是赫施节点线反铁磁体。
英文摘要
Recently, a new class of Weyl semimetals in antiferromagnets named Heesch Weyl semimetals was discovered, which have inadmissible chiral magnetic point group symmetries (inadmissible magnetic point groups are incompatible with ferromagnetic order) and distinctive surface Fermi arcs. In Heesch Weyl semimetals, the Weyl points are pinned at high symmetry momenta with two-dimensional irreducible corepresentations in the Brillouin zone. As the Weyl points are pinned, the Weyl points with opposite topological charges cannot emerge or be brought together for creation and annihilation as in conventional Weyl semimetals. In this work, we show that when mirror or rotoinversion symmetries are restored so that the point group becomes achiral, long doubly degenerate lines connecting Weyl points with opposite topological charges emerge. We call these lines the Heesch nodal lines (HNLs) and their host materials the Heesch nodal line antiferromagnets. HNLs result in a large number of two-dimensional massless Dirac cones for planes intercepting the HNLs in the Brillouin zone. Moreover, a large subset of the HNL antiferromagnets has the special property that the lowest nonvanishing order of the nonlinear anomalous Hall effect starts with the third order. First-principles calculations on representative collinear and noncollinear antiferromagnets, such as MnTe, CrSb, and Mn$_3$GaN, confirm our predictions on the presence of HNLs. When the inadmissible symmetry is broken by strain, the double degeneracy of the HNLs is lifted and the associated massless Dirac cones are gapped out, providing a route to realizing sizable anomalous Hall effects in antiferromagnetic crystals. We conclude that all inadmissible antiferromagnets without parity-time symmetry are topological. They are either Heesch Weyl antiferromagnets or Heesch nodal line antiferromagnets.
Comments19 pages, 6 figures, and 4 tables, including Supplementary Information
