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arXiv 1407.2152cond-mat.mes-hall
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量子霍尔效应与量子自旋霍尔效应的动力学竞争

Dynamical competition between Quantum Hall and Quantum Spin Hall effects

Anton Quelle, Cristiane Morais Smith

摘要:

本文研究非等熵拓扑系统中量子相变的发生。更具体地说,我们考虑石墨烯与一个相当大的自旋轨道耦合,照射圆偏振光。在没有光的情况下,自旋轨道耦合驱动量子自旋霍尔相位,其中具有相反自旋的边缘电流反向传播。另一方面,光产生一个依赖于时间的矢量势,这导致了一个跳跃参数与交错的苯环周围的依赖于时间的相位。该模型是一个动力学版本的Halfton模型,它认为一个静态交错通量与零总通量通过每个plaquette。由于光打破了时间反演对称性,一个由整数拓扑不变量保护的量子霍尔相位出现了。通过数值求解完整的问题,自旋轨道耦合和光,并研究不同的驱动频率ω的值,我们表明,光谱表现出非平凡的差距不仅在零能量,而且在ω/2。这个额外的间隙是由石墨烯的价带和导带之间的光子共振产生的,并且光谱的对称性迫使它位于ω/2。通过增加辐照强度,零能隙中的拓扑态经历了从量子自旋霍尔到量子霍尔相的动态相变,而ω/2附近的能隙保持在量子霍尔区。

英文摘要:

In this paper we investigate the occurrence of quantum phase transitions in topological systems out of equi- librium. More specifically, we consider graphene with a sizable spin-orbit coupling, irradiated by circularly- polarized light. In the absence of light, the spin-orbit coupling drives a quantum spin Hall phase where edge currents with opposite spins counter-propagate. On the other hand, the light generates a time-dependent vector potential, which leads to a hopping parameter with staggered time-dependent phases around the benzene ring. The model is a dynamical version of the Haldane model, which considers a static staggered flux with zero total flux through each plaquette. Since the light breaks time-reversal symmetry, a quantum Hall phase protected by an integer topological invariant arises. By numerically solving the complete problem, with spin-orbit coupling and light, and investigating different values of the driving frequency ω, we show that the spectrum exhibits non-trivial gaps not only at zero energy, but also at ω/2. This additional gap is created by photon resonances between the valence and conduction band of graphene, and the symmetry of the spectrum forces it to lie at ω/2. By increasing the intensity of the irradiation, the topological state in the zero energy gap undergoes a dynamical phase transition from a quantum spin Hall to a quantum Hall phase, whereas the gap around ω/2 remains in the quantum Hall regime.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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