用协方差噪声磁强计探测非局域超导涨落
Probing nonlocal superconducting fluctuations with covariance noise magnetometry
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中文总结 AI 辅助
研究利用含时金兹堡-朗道框架计算非局域超导涨落修正对电导率张量的影响，通过单个NV传感器和双传感器协方差磁强计分析相关特性，求解波动薄膜非平衡电流噪声，结果与BSCCO薄膜电流噪声实验相关。
中文摘要 AI 辅助
在含时金兹堡-朗道框架内计算了电导率张量\(\sigma_{ij}(\mathbf{q},\omega)\)的非局域超导涨落修正，并研究了其对量子噪声磁强计的可观测影响。对于单个氮空位（NV）传感器，得到了弛豫率\(1/T_1\)与温度、样品-传感器距离和探测频率的函数关系，确定了非局域性和对涨落动力学切断\(T_c\)附近临界增强的尺度。对于双传感器协方差磁强计，表明两点场关联器发展出额外的空间结构，其范围直接测量涨落关联长度\(\xi(T)\)。还分析了伴随顺磁导率的两个通道：对自旋磁化率的牧木-汤普森修正和涨落抗磁性。最后，精确求解了波动薄膜在直流电场和所有波矢下的非平衡电流噪声：噪声与非线性顺磁导率解耦，在临界处违反涨落-耗散定理，获得由协方差磁强计直接测量的偏置诱导空间各向异性。结果与最近测量BSCCO薄膜附近电流噪声的实验相关。
英文摘要
The nonlocal superconducting fluctuation corrections to the conductivity tensor $σ_{ij}(\mathbf{q},ω)$ are calculated within the time-dependent Ginzburg-Landau framework, and their observable consequences for quantum noise magnetometry are worked out. For a single nitrogen-vacancy (NV) sensor we obtain the relaxation rate $1/T_1$ as a function of temperature, sample-sensor distance, and probe frequency, identifying the scales at which the nonlocality and the dynamics of the pair fluctuations cut off the critical enhancement near $T_c$. For two-sensor covariance magnetometry we show that the two-point field correlator develops additional spatial structure whose range directly measures the fluctuation correlation length $ξ(T)$. We further analyze two channels that accompany the paraconductivity: the Maki-Thompson correction to the spin susceptibility, and the fluctuation diamagnetism. Finally, we solve exactly, to all orders in a dc electric field and at all wave vectors, for the nonequilibrium current noise of the fluctuating film: the noise decouples from the nonlinear paraconductivity, violating the fluctuation-dissipation theorem by universal factors at criticality and acquiring a bias-induced spatial anisotropy directly measurable by covariance magnetometry. The results are connected to a recent experiment measuring current noise near a thin film of BSCCO.
