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arXiv 1201.4095cond-mat.mes-hallcond-mat.otherhep-th
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拓扑绝缘体中的引力反常和热霍尔效应

Gravitational Anomalies and Thermal Hall effect in Topological Insulators

Michael Stone

摘要:

有人提出,温度梯度会在DIII类拓扑绝缘体表面的马约拉纳准粒子中诱导出Leduc-Righi或热霍尔电流,并且该电流的大小可以通过爱因斯坦变元{ \it via}与引力诱导的霍尔能流相关联。我们批判性地研究了这个想法,并认为引力霍尔效应比它熟悉的类似物更复杂。传统的霍尔电流是由{ \it uniform}电场产生的,但从引力Chern-Simons泛函计算通量表明,引力场{ \it梯度} -即潮汐力-需要诱导能量动量流。我们将表面能动量通量与畴壁引力异常{ \it via}的Callan-Harvey入流机制联系起来。我们强调,结合体加边界理论的规范不变性,确保在畴壁的电流总是经历一个“协变”,而不是“一致”的异常。我们利用这一观测结果证实了潮汐引起的能量-动量流可以精确地解释$(1+1)$维畴壁费米子中的协变引力异常。无论我们用克里斯托夫勒符号还是用自旋联系来写陈-西蒙斯泛函,都会出现同样的反常现象。

英文摘要:

It has been suggested that a temperature gradient will induce a Leduc-Righi, or thermal Hall, current in the Majorana quasiparticles localized on the surface of class DIII topological insulators, and that the magnitude of this current can be related {\it via} an Einstein argument to a Hall-like energy flux induced by gravity. We critically examine this idea, and argue that the gravitational Hall effect is more complicated than its familiar analogue. A conventional Hall current is generated by a {\it uniform} electric field, but computing the flux from the gravitational Chern-Simons functional shows that gravitational field {\it gradients} - i.e. tidal forces - are needed to induce a energy-momentum flow. We relate the surface energy-momentum flux to a domain-wall gravitational anomaly {\it via} the Callan-Harvey inflow mechanism. We stress that the gauge invariance of the combined bulk-plus-boundary theory ensures that the current in the domain wall always experiences a "covariant" rather than "consistent" anomaly. We use this observation to confirm that the tidally induced energy-momentum current exactly accounts for the covariant gravitational anomaly in $(1+1)$ dimensional domain-wall fermions. The same anomaly arises whether we write the Chern-Simons functional in terms of the Christofflel symbol or in terms of the the spin connection.

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