用真实脉冲驱动的拓扑系统的光导率
Optical conductivity of a topological system driven using a realistic pulse
AI总结：
本研究受泵浦-探测技术启发，考虑非纯周期性脉冲驱动的拓扑系统光学响应，用实时演化态计算光导率并与Floquet理论结果比较，发现光导率保留初始平衡态记忆，Floquet带布居由其与初始态重叠决定且在布里渊区能带反转点布居也反转。
摘要：
在Floquet理论的框架下，人们研究了时间周期扰动（如辐射）对原本处于平衡状态的系统的影响，其中定态被Floquet态取代，能量被准能取代。这些准能带通常在色散上与能带有差异，特别是在存在自旋轨道耦合的情况下，其状态也不同。当准能带表现出与定态对应物不同的拓扑不变量时，在某些情况下这可能会改变拓扑结构。在这项工作中，受泵浦-探测技术进展的启发，我们考虑了驱动拓扑系统的光学响应，此时驱动不是纯周期性的，而是乘以了脉冲形状/包络函数。我们使用实时演化态来计算光导率，并将其与使用Floquet理论计算的响应进行比较。我们发现，即使泵浦缓慢开启且测量在斜坡后很久进行，光导率仍保留初始平衡态的记忆。时间演化系统的响应被解释为来自Floquet带，其布居由它们与初始平衡态的重叠决定。特别是在布里渊区的能带反转点，Floquet带的布居也会反转。
英文摘要：
The effect of a time-periodic perturbation, such as radiation, on a system otherwise at equilibrium has been studied in the context of Floquet theory with stationary states replaced by Floquet states and the energy replaced by quasienergy. These quasienergy bands in general differ from the energy bands in their dispersion and, especially in the presence of spin-orbit coupling, in their states. This may, in some cases, alter the topology when the quasienergy bands exhibit different topological invariants than their stationary counterparts. In this work, motivated by advances in pump-probe techniques, we consider the optical response of driven topological systems when the drive is not purely periodic but is instead multiplied by a pulse shape/envelope function. We use real time-evolved states to calculate the optical conductivity and compare it to the response calculated using Floquet theory. We find that the conductivity bears a memory of the initial equilibrium state even when the pump is turned on slowly and the measurement is taken well after the ramp. The response of the time-evolved system is interpreted as coming from Floquet bands whose population has been determined by their overlap with the initial equilibrium state. In particular, at band inversion points in the Brillouin zone the population of the Floquet bands is inverted as well.
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