The Critical Current of Disordered Superconductors near T=0

Abstract

An increasing current through a superconductor can result in a discontinuous increase in the differential resistance at the critical current. This critical current is typically associated either with breaking of Cooper-pairs (de-pairing) or with a collective motion of vortices (de-pinning). In this work we measure superconducting amorphous indium oxide films at low temperatures and high magnetic fields. Using heat-balance considerations we demonstrate that the current-voltage characteristics are well explained by electron overheating that occurs due to the thermal decoupling of the electrons from the host phonons. As a result the electrons overheat to a significantly higher temperature than that of the lattice. By solving the heat-balance equation we are able to accurately predict the critical currents in a variety of experimental conditions. The heat-balance approach stems directly from energy conservation. As such it is universal and applies to diverse situations from critical currents in superconductors to climate bi-stabilities that can initiate another ice-age. One disadvantage of the universal nature of this approach is that it is insensitive to the microscopic details of the system, which limits our ability to draw conclusions regarding the initial departure from equilibrium.

Limited role of vortices in transport in highly disordered superconductors near $B_{c2}$

“…This result is consistent with the conclusions of Ref. [13] where we showed that the critical currents are determined entirely by the Ohmic…”

“…Adding to that the aforementioned result reported in Ref. [13], that J || c is independent of the angle ϕ between J and B || , suggests that the finite R and J c measured in our type-II superconductor at a finite T is caused by a non-vortex mechanism and raises the interesting question of what actually causes R in highly disordered superconductors near B c2 .…”

“…S2 of the supplemental material of Ref. [13] which uses experimental results of Refs. [39,42]), the mean-free path is smaller than 1nm, the magnetic length corresponding to B 0 in samples thicker than 57nm is 19nm and in the 22nm and 26nm thick samples it is 12nm.…”

“…As λ t in our type-II superconductor, λ ⊥ λ. Recently, we studied the critical current (I c ) in a:InO films at low T 's and high B's near B c2 [13] and showed that I c is consistent with a thermal bi-stability. To study the contribution of vortex motion to I c we measured…”