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首页> 外文期刊>Physical review >Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator
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Out-of-equilibrium electrons and the Hall conductance of a Floquet topological insulator

机译：非平衡电子和Floquet拓扑绝缘体的霍尔电导

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摘要

Graphene irradiated by a circularly polarized laser has been predicted to be a Floquet topological insulator showing a laser-induced quantum Hall effect. A circularly polarized laser also drives the system out of equilibrium, resulting in nonthermal electron distribution functions that strongly affect transport properties. Results are presented for the Hall conductance for two different cases. One is for a closed system, such as a cold-atomic gas, where transverse drift due to nonzero Berry curvature can be measured in time-of-flight measurements. For this case the effect of a circularly polarized laser that has been suddenly switched on is studied. The second is for an open system coupled to an external reservoir of phonons. While for the former the Hall conductance is far from the quantized limit, for the latter, coupling to a sufficiently low temperature reservoir of phonons is found to produce effective cooling, and thus an approach to the quantum limit, provided the frequency of the laser is large as compared to the bandwidth. For laser frequencies comparable to the bandwidth, strong deviations from the quantum limit of conductance are found even for a very low temperature reservoir, with the precise value of the Hall conductance determined by a competition between reservoir-induced cooling and the excitation of photocarriers by the laser. For the closed system, the electron distribution function is determined by the overlap between the initial wave function and the Floquet states, which can result in a Hall conductance which is opposite in sign to that of the open system.
机译：圆偏振激光辐照的石墨烯已被预测为Floquet拓扑绝缘体，显示出激光诱导的量子霍尔效应。圆偏振激光器还会使系统失衡，导致非热电子分布功能严重影响传输性能。给出了两种情况下霍尔电导的结果。一种是用于封闭系统，例如冷原子气体，其中可以在飞行时间测量中测量由于非零贝里曲率引起的横向漂移。对于这种情况，研究了突然打开的圆偏振激光器的效果。第二个是用于与声子的外部容器耦合的开放系统。对于前者，霍尔电导远未达到量化极限，而对于后者，发现耦合至足够低的声子温度储集层可产生有效的冷却，因此，只要激光的频率为与带宽相比更大。对于与带宽相当的激光频率，即使对于温度非常低的储层，也发现与电导的量子极限有很大的偏差，霍尔电导的精确值由储层诱导的冷却与光载体的激发之间的竞争决定。激光。对于封闭系统，电子分布函数由初始波函数和Floquet状态之间的重叠确定，这可能导致霍尔电导与开放系统的符号相反。

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