论文标题
离散的全球对称性和新兴费米子的动态
Discrete global symmetries and dynamics of emergent fermions
论文作者
论文摘要
定义低能自由度数量的全球对称性对拓扑量子临界点附近以及其他不合格性或几乎无间隙状态的普遍性产生了深远的影响。我们以$ Z_2 $的全球对称性（例如时间逆转）为例，以研究其对热力学和运输特性的影响。尽管$ z_2 $对称系统的热熵密度仅仅是其同行的两倍，而没有任何全球对称性或$ z_1 $ class，但对于不同的对称性，热导率的温度依赖性$κ$明显不同。对于具有动态指数$ z = 1 $的系统，在$ z_2 $对称类中，我们在量子关键方案中有$κ\ propto t^{ - （d-1）} $接近弱相互交互的固定点，而对于没有全球对称性的系统，而没有全球对称性的系统 方面。只有靠近强的耦合固定点，带有或不带有$ z_2 $ global对称性的两个情况都遵循相同的缩放函数，$κ\ propto t^{d-1} $。这些独特的热导率尺度也可以出现在无间隙的表面主要状态。
Global symmetries that define the number of low energy degrees of freedom have profound consequences on universal properties near topological quantum critical points and in other gapless or nearly gapless states of emergent fermions. We take a $Z_2$ global symmetry (such as time-reversal) as an example to study its effect on thermodynamic and transport properties. Although the thermal entropy density of $Z_2$ symmetric systems is simply twice of their counterparts without any global symmetries or the $Z_1$ class, the temperature dependence of thermal conductivity $κ$ is distinctly and drastically different for different symmetries. For systems with dynamic exponent $z=1$, in the $Z_2$ symmetric class, we have $κ\propto T^{-(d-1)}$ in the quantum critical regime near weakly interacting fixed points, while for systems with no global symmetries (i.e., the $Z_1$ class), we have $κ\propto T^{-(d+3)}$, with $d$ being the spatial dimension. Only near strong coupling fixed points, both cases with or without $Z_2$ global symmetries follow the same scaling function, $κ\propto T^{d-1}$. These distinct scalings of thermal conductivity can also appear in gapless surface Majorana states.
