New paradigm for superconductivity in a disordered vortex lattice

Orbital magnetic field, as well as disorder, weaken superconductivity when acting individually on a type-II s-wave superconductor. The Abrikosov vortex lattice in a clean type-II superconductor, resulting from an orbital magnetic field, transforms into a metal beyond a critical magnetic field $H_c$ once vortices start overlapping. Similarly, disorder drives a transition from a superconductor to a paired insulator beyond a critical disorder strength. Here we show that acting simultaneously in a two-dimensional superconductor, disorder and magnetic field lead to an intriguing evolution of the superconducting state. While for weak disorder, the critical field $H_c$ for the suppression of superconducting energy gap matches the critical field at which the superfluid density collapses, the two critical fields diverge from each other with increasing disorder creating a pseudogap region. Our phase diagram of the supercondutor in the plane of disorder and magnetic field provide a natural explanation of the long standing puzzle of the gigantic magnetoresistance peak observed at large magnetic fields in thin films of disordered superconducting. We illustrate this by calculating the dynamical conductivity using Kubo formula and analyzing its low-frequency behavior. We also demonstrate that the presence of even weak disorder causes the Caroli-deGennes-Matricon peak near zero-bias in the local density of states at the vortex-core to disappear. The origin and consequences of such dramatic behaviors will be discussed along with their experimental relevance.

(https://arxiv.org/abs/2101.00220)