在松弛时间近似下，该研究团队得到了时间反演和三角对称的能带投影理论中电流驱动场的无限阶解析表达式。对于固定场强，用玫瑰线给出了电流随外加场方向的依赖关系，玫瑰线的花瓣结构是对称约束的，由实空间平移向量展开得到。研究人员通过周期性屈曲石墨烯和扭曲双层石墨烯的计算来说明他们的理论，其中所讨论的物理可以在实验相关的场强下获得。
据悉，在二维人工晶体中具有大实空间周期性的情况下，外加大电场会导致非线性电流响应，并且这种响应具有很强的角度依赖性。这种角度依赖性编码了孤立电子布洛赫微带的能带色散和贝里曲率信息。
附：英文原文
Title: Roses in the nonperturbative current response of artificial crystals
Author: De Beule, Christophe, Phong, V Tin, Mele, E. J.
Issue&Volume: 2023-10-19
Abstract: In two-dimensional artificial crystals with large real-space periodicity, the nonlinear current response to a large applied electric field can feature a strong angular dependence, which encodes information about the band dispersion and Berry curvature of isolated electronic Bloch minibands. Within the relaxation-time approximation, we obtain analytic expressions up to infinite order in the driving field for the current in a band-projected theory with time-reversal and trigonal symmetry. For a fixed field strength, the dependence of the current on the direction of the applied field is given by rose curves whose petal structure is symmetry constrained and is obtained from an expansion in real-space translation vectors. We illustrate our theory with calculations on periodically buckled graphene and twisted double bilayer graphene, wherein the discussed physics can be accessed at experimentally relevant field strengths.
DOI: 10.1073/pnas.2306384120
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2306384120