Universal scaling behaviour near vortex-solid/glass to vortex-fluid transition in type-II superconductors in two- and three-dimensions

TL;DR

This study investigates the vortex-solid/glass to vortex-fluid transition in NbN superconductors, revealing dimensional differences in phase diagram behavior and critical exponents through magnetoresistance and current-voltage measurements.

Contribution

It provides the first comparative analysis of vortex phase transitions in 2D and 3D NbN superconductors using independent dynamical exponent measurements.

Findings

3D NbN shows consistent critical exponents from different measurements.

2D NbN exhibits divergent exponents, indicating different scaling behavior.

The phase diagram near the critical point differs significantly between 2D and 3D NbN.

Abstract

In this article, we present evidence for the existence of vortex-solid/glass (VG) to vortex-fluid (VF) transition in a type-II superconductor (SC), NbN. We probed the VG to VF transition in both 2D and 3D films of NbN through studies of magnetoresistance and current-voltage characteristics. The dynamical exponents corresponding to this phase transition were extracted independently from the two sets of measurements. The $H$-$T$ phase diagram for the 2D and 3D SC are found to be significantly different near the critical point. In the case of 3D SC, the exponent values obtained from the two independent measurements show excellent match. On the other hand, for the 2D SC, the exponents obtained from the two experiments were significantly different. We attribute this to the fact that the characteristic length scale diverges near the critical point in a 2D SC in a distinctly different way from its 3D counterpart form scaling behaviour.