In this Rapid Communication we investigate the fluctuation effects on the transport properties of unitary Fermi gases in the vicinity of the superfluid transition temperature ${T}_{\mathrm{c}}$ . Based on the time-dependent Ginzburg-Landau formalism of the Bose-Einstein condensate--BCS crossover, we investigate both the residual resistivity below ${T}_{\mathrm{c}}$ induced by phase slips and the paraconductivity above ${T}_{\mathrm{c}}$ due to pair fluctuations. These two effects have been well studied in the weak-coupling BCS superconductor and here we generalize them to the unitary regime of ultracold Fermi gases. We find that while the residual resistivity below ${T}_{\mathrm{c}}$ increases as one approaches the unitary limit, consistent with recent experiments, the paraconductivity exhibits nonmonotonic behavior. Our results can be verified with the recently developed transport apparatus using mesoscopic channels.In this Rapid Communication we investigate the fluctuation effects on the transport properties of unitary Fermi gases in the vicinity of the superfluid transition temperature ${T}_{\mathrm{c}}$. Based on the time-dependent Ginzburg-Landau formalism of the Bose-Einstein condensate--BCS crossover, we investigate both the residual resistivity below ${T}_{\mathrm{c}}$ induced by phase slips and the paraconductivity above ${T}_{\mathrm{c}}$ due to pair fluctuations. These two effects have been well studied in the weak-coupling BCS superconductor and here we generalize them to the unitary regime of ultracold Fermi gases. We find that while the residual resistivity below ${T}_{\mathrm{c}}$ increases as one approaches the unitary limit, consistent with recent experiments, the paraconductivity exhibits nonmonotonic behavior. Our results can be verified with the recently developed transport apparatus using mesoscopic channels.

arXiv:1408.4557Physical Review ANov 21, 201412 citations

Radio-frequency spectroscopy of ultracold atomic Fermi gases

André Schirotzek

Jan 1, 20103 citations

Probing nonlocal superconducting fluctuations with covariance noise magnetometry

Gustav Romare, Ilya Esterlis, Shimon Kolkowitz +1 more

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.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.

cond-mat.supr-conCross-listedarXiv:2607.24906Jul 29, 2026

Fluctuations and correlations in ultracold Fermi gases

Jan Jakob Meineke

Jan 1, 20121 citation

In this Rapid Communication we investigate the fluctuation effects on the transport properties of unitary Fermi gases in the vicinity of the superfluid transition temperature

{T}_{\mathrm{c}}

. Based on the time-dependent Ginzburg-Landau formalism of the Bose-Einstein condensate--BCS crossover, we investigate both the residual resistivity below

{T}_{\mathrm{c}}

induced by phase slips and the paraconductivity above

{T}_{\mathrm{c}}

due to pair fluctuations. These two effects have been well studied in the weak-coupling BCS superconductor and here we generalize them to the unitary regime of ultracold Fermi gases. We find that while the residual resistivity below

{T}_{\mathrm{c}}

increases as one approaches the unitary limit, consistent with recent experiments, the paraconductivity exhibits nonmonotonic behavior. Our results can be verified with the recently developed transport apparatus using mesoscopic channels.

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.