Weyl半金属中的磁催化和轴子电荷密度波
Magnetic catalysis and axionic charge-density-wave in Weyl semimetals
摘要：
三维Weyl和Dirac半金属在强磁场中，即使电子-电子相互作用足够弱，也能支持手征对称破缺、完全带隙的电荷密度波序。在前一种系统中，由于外尔节点的自然动量空间分离，有序相缺乏平移对称性，代表物质的轴子相，而狄拉克半金属中的有序相（忽略塞曼耦合）只是平凡的绝缘体。我们提出了一个广泛的亚临界（弱）相互作用，以及与磁场的抗磁化率的光谱间隙的缩放。一个类似的机制，电荷密度波排序在弱耦合被证明是有效的双和三重Weyl半金属，其中的色散是线性的（二次和三次，分别）的z（平面）分量（S）的动量。我们还讨论了电荷密度波阶数和自旋密度波阶数之间的竞争，这两种阶数都破坏了手征对称性并导致能隙谱，并表明至少在弱耦合区，前者在能量上是有利的。异常的表面霍尔电导率，拓扑缺陷的作用，如轴子弦，一维无隙色散模式的存在，沿这种缺陷的核心，和异常取消通过Callan-Harvey机制进行了讨论。
英文摘要：
Three-dimensional Weyl and Dirac semimetals can support a chiral-symmetry-breaking, fully gapped, charge-density-wave order even for sufficiently weak repulsive electron-electron interactions, when placed in strong magnetic fields. In the former systems, due to the natural momentum space separation of Weyl nodes the ordered phase lacks the translational symmetry and represents an axionic phase of matter, while that in a Dirac semimetal (neglecting the Zeeman coupling) is only a trivial insulator. We present the scaling of this spectral gap for a wide range of subcritical (weak) interactions as well as that of the diamagnetic susceptibility with the magnetic field. A similar mechanism for charge-density-wave ordering at weak coupling is shown to be operative in double and triple-Weyl semimetals, where the dispersion is linear (quadratic and cubic, respectively) for the z (planar) component(s) of the momentum. We here also address the competition between the charge-density-wave and a spin-density-wave orders, both of which breaks the chiral symmetry and leads to gapped spectrum, and show that at least in the weak coupling regime the former is energetically favored. The anomalous surface Hall conductivity, role of topological defects such as axion strings, existence of one-dimensional gapless dispersive modes along the core of such defects, and anomaly cancellation through the Callan-Harvey mechanism are discussed.
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