AI 中文总结
该研究建立二维非中心对称超导体涨落区的非线性光学与输运响应理论，推导相关电流通道公式，揭示对称性对非线性电流的决定作用及实验分离各通道的方法。
AI 中文摘要
我们发展了二维非中心对称超导体在相变温度以上涨落区域的非线性光学与输运响应理论，涵盖光电流效应、二次谐波产生和光伏霍尔效应。在相变附近，这些响应被预形成的库珀对显著增强，其非互易性通过两种物理上不同的方式进入含时金兹堡-朗道描述：一是热力学利夫希茨不变量，编码非对称的对谱；二是动力学利夫希茨不变量，编码非对称的对弛豫，并通过涨落-耗散定理与朗之万噪声锁定。我们推导了非线性电流的顺电导（Aslamazov-Larkin）通道和量子干涉（Maki-Thompson）通道的广义主公式，适用于任意驱动频率且为非互易微扰的线性阶，并将其简化为闭合形式的无量纲函数。圆偏振光可显著区分这些机制：对于无动量结构的互易噪声，Aslamazov-Larkin通道对偏振不敏感，其圆偏光电流响应在任何对谱下均消失；而Maki-Thompson通道和非互易噪声支持螺旋度奇宇称的整流电流，包括垂直于应变轴流动的涨落光伏霍尔电流。对Rashba型（C₃ᵥ）和Ising型（D₃ₕ）超导体的应用表明，点群对称性如何决定非线性电流的允许矢量结构，以及偏振分析结合频率和退相依性如何可用于实验上分离各通道。
英文摘要
We develop a theory of the nonlinear optical and transport responses of two-dimensional noncentrosymmetric superconductors in the fluctuation regime above the transition temperature, encompassing the photogalvanic effect, second-harmonic generation, and the photovoltaic Hall effect. In the vicinity of the transition these responses are strongly enhanced by preformed Cooper pairs, whose nonreciprocity enters the time-dependent Ginzburg-Landau description in two physically distinct ways: through thermodynamic Lifshitz invariants, which encode an asymmetric pair spectrum, and through kinetic Lifshitz invariants, which encode an asymmetric pair relaxation and are locked to the Langevin noise by the fluctuation-dissipation theorem. We derive generalized master formulas for the paraconductivity (Aslamazov-Larkin) and the quantum-interference (Maki-Thompson) channels of the nonlinear current, valid at arbitrary drive frequency and to linear order in the nonreciprocal perturbations, and reduce them to closed-form dimensionless functions. Circular polarization discriminates sharply between the mechanisms: for reciprocal momentum-structureless noise the Aslamazov-Larkin channel is polarization insensitive and its circular photogalvanic response vanishes for any pair spectrum, whereas the Maki-Thompson channel and the nonreciprocal noise support helicity-odd rectified currents, including a fluctuation photovoltaic Hall current flowing transverse to the strain axis. Applications to Rashba-type ($C_{3v}$) and Ising-type ($D_{3h}$) superconductors demonstrate how the point-group symmetry dictates the allowed vector structures of the nonlinear currents, and how polarization analysis together with the frequency and dephasing dependences can be used to separate the individual channels experimentally.
Comments30 pages, 6 figures
