Superconducting fluctuations in a thin NbN film probed by the Hall effect

Abstract

We present a comprehensive study of how superconducting fluctuations in the normal state contribute to the conductivity tensor in a thin (119 $\tilde{A}$) film of NbN. It is shown how these fluctuations drive a sign change in the Hall coefficient $R_{\mathrm{H}}$ for low magnetic fields near the superconducting transition. The scaling behaviours as a function of distance to the transition $\hat{I}\mu =\ln (T/T_{\mathrm{c}})$ of the longitudinal ($\ddot{I}{ƒ}_{\mathrm{xx}}$) and transverse ($\ddot{I}{ƒ}_{\mathrm{xy}}$) conductivity is found to be consistent with Gaussian fluctuation theory. Moreover, excellent quantitative agreement between theory and experiment is obtained without any adjustable parameters. Our experimental results thus provide a case study of the conductivity tensor originating from short-lived Cooper pairs.

6 pages, 4 figures