Paraconductivity of pseudogapped superconductors

Abstract

We calculate Aslamazov-Larkin paraconductity $\sigma_{AL}(T)$ for a model of strongly disordered superconductors (dimensions $d=2,3$) with a large pseudogap whose magnitude strongly exceeds transition temperature $T_c$. We show that, within Gaussian approximation over Cooper-pair fluctuations, paraconductivity is just twice larger that the classical AL result at the same $\epsilon = (T-T_c)/T_c$. Upon decreasing $\epsilon$, Gaussian approximation is violated due to local fluctuations of pairing fields that become relevant at $\epsilon \leq \epsilon_1 \ll 1 $. Characteristic scale $\epsilon_1 $ is much larger than the width $\epsilon_2$ of the thermodynamical critical region, that is determined via the Ginzburg criterion, $\epsilon_2 \approx \epsilon_1^d$. We argue that in the intermediate region $\epsilon_2 \leq \epsilon \leq \epsilon_1$ paraconductivity follows the same AL power law, albeit with another (yet unknown) numerical prefactor. At further decrease of the temperature, all kinds of fluctuational corrections become strong at $\epsilon \leq \epsilon_2$; in particular, conductivity occurs to be strongly inhomogeneous in real space.