Probing nonlocal superconducting fluctuations with covariance noise magnetometry

Abstract:The nonlocal superconducting fluctuation corrections to the conductivity tensor $\sigma_{ij}(\mathbf{q},\omega)$ 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 $\xi(T)$. 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.

Superconductivity (cond-mat.supr-con); Quantum Physics (quant-ph)

arXiv:2607.24906 [cond-mat.supr-con]

(or arXiv:2607.24906v1 [cond-mat.supr-con] for this version)

https://doi.org/10.48550/arXiv.2607.24906 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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