# Non-linear $IV$ characteristics in two-dimensional superconductors: Berezinskii-Kosterlitz-Thouless physics vs inhomogeneity

## TL;DR

This paper compares $IV$ characteristics in two 2D superconductors, NbN and SrTiO$_3$ interfaces, revealing BKT physics in one and inhomogeneity effects in the other, challenging traditional interpretations.

## Contribution

It demonstrates that non-linear $IV$ behavior in 2D superconductors can arise from inhomogeneity rather than solely from BKT physics.

## Key findings

- NbN exhibits BKT-like non-linear effects in $IV$ characteristics.
- SrTiO$_3$ interfaces' $IV$ behavior is explained by mesoscopic inhomogeneity.
- Inhomogeneity can mimic BKT signatures in 2D superconductors.

## Abstract

One of the hallmarks of the Berezinskii-Kosterlitz-Thouless (BKT) transition in two-dimensional (2D) superconductors is the universal jump of the superfluid density, that can be indirectly probed via the non-linear exponent of the current-voltage $IV$ characteristics. Here, we compare the experimental measurements of $IV$ characteristics in two cases, namely NbN thin films and SrTiO$_3$-based interfaces. While the former display a paradigmatic example of BKT-like non-linear effects, the latter do not seem to justify a BKT analysis. Rather, the observed $IV$ characteristics can be well reproduced theoretically by modelling the effect of mesoscopic inhomogeneity of the superconducting state. Our results offer an alternative perspective on the spontaneous fragmentation of the superconducting background in confined 2D systems.