双色圆偏振场驱动的能谷极化：旋转坐标系与强场视角
Valley polarization driven by two-color circular fields: a rotating frame and strong-field perspective
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中文总结 AI 辅助
本研究针对六方材料中依赖光场取向的能谷极化现象，从强场隧穿动力学和旋转坐标系弱场两个互补视角展开理论推导，揭示了能谷极化的新机制，拓展了能谷调控的适用范围。
中文摘要 AI 辅助
近期理论与实验均已证实，六方材料中的能谷极化由光波的形式及其相对于晶格的取向驱动，而非仅由驱动光的螺旋度决定。这一发现将能谷调控拓展到了非共振、亚周期区间以及反演对称材料中。对于这种依赖场取向的能谷极化，一种解释是：通过Floquet类方法得到的激光修饰的、周期平均的能带结构发生了改变，从而解除了能谷之间的简并。本文基于强场隧穿动力学推导了一种互补的解释。我们表明，在主要注入时刻的有效能谷带隙通过低能色散的三角翘曲项依赖于场相对于晶格的取向。我们推导了同向旋转和反向旋转ω+Nω场的通用表达式，并表明仅当场构型与三重晶格对称性兼容时，主导的取向相关贡献才会在周期平均后保留，最显著的是反向旋转ω+2ω场和同向旋转ω+4ω场。作为一项互补的弱场结果，我们表明，对于反向旋转双圆场，单光子能谷选择定则可以表示为旋转坐标系中依赖于能谷的能量失谐，在该坐标系中两种色光获得相同的频率。
英文摘要
Valley polarization in hexagonal materials driven by the form of the lightwave and its orientation relative to the lattice, rather than solely by the helicity of the driver, has recently been demonstrated both theoretically and experimentally. This has extended valley control to the non-resonant, sub-cycle regime and to inversion-symmetric materials. One interpretation of this field-orientation-dependent valley polarization is that the laser-dressed, cycle-averaged band structure obtained from a Floquet-type approach is modified so as to lift the degeneracy between the valleys. Here, we derive a complementary explanation based on strong-field tunneling dynamics. We show that the effective valley gap at the dominant injection times depends on the orientation of the field relative to the lattice through the trigonal-warping term of the low-energy dispersion. We derive general expressions for co- and counter-rotating $ω+Nω$ fields and show that the leading orientation-dependent contribution survives the cycle average only for field configurations compatible with the threefold lattice symmetry, most notably counter-rotating $ω+2ω$ and co-rotating $ω+4ω$ fields. As a complementary weak-field result, we show that, for counter-rotating bicircular fields, the one-photon valley selection rules can be represented as valley-dependent energy detunings in a rotating frame where both colors acquire the same frequency.
