Weyl-semimetal superstructures with a spiraling position of a pair of Weyl nodes of opposite chirality can host a chiral-symmetry-preserving Fermi-arc metal state, where the chirality is carried by cylindrical Fermi surfaces, electronlike and holelike depending on the chirality. The Fermi surfaces nest at vanishing momentum separation (zero nesting vector) at the electron-hole-compensation energy because the nesting is topologically protected by vanishing spatial overlap of any pair of equal-momentum opposite-chirality states. In this work we show that the nesting and Coulomb interaction drive a spontaneous chiral symmetry breaking in such a Fermi-arc metal, which leads to a dynamical axion insulator state but without breaking translational symmetry (no charge-density-wave order) as in a conventional Weyl semimetal. As for material realization, we discuss magnetically doped ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, for which the Weyl-node positions depend on the order of the magnetic dopands. In this case, the axionic condensation can itself stabilize a spiral order of the magnetization, and hence the spiraling node positions, even if the magnetic interaction is intrinsically ferromagnetic.

中文翻译：

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周期性Weyl半金属超结构的轴离子不稳定性

具有一对相反手性的外尔节点的螺旋位置的外尔半金属超结构可以容纳手性对称性保持的费米弧金属态，其中手性由圆柱形费米表面携带，电子状和孔状取决于手性。费米面在电子空穴补偿能量处以消失动量分离（零嵌套矢量）嵌套，因为嵌套受到任何一对等动量相反手性态的消失空间重叠的拓扑保护。在这项工作中，我们表明，嵌套和库仑相互作用驱动这种费米弧金属中的自发手性对称性破缺，从而导致动态轴子绝缘体状态，但不会破坏平移对称性（无电荷密度波序），就像在传统的韦尔半金属。至于材料实现，我们讨论磁掺杂${双}_2{硒}_3$，其中韦尔节点位置取决于磁性掺杂剂的顺序。在这种情况下，轴离子凝聚本身可以稳定磁化的螺旋顺序，从而稳定螺旋节点位置，即使磁相互作用本质上是铁磁的。