# London penetration depth and thermal fluctuations in the sulphur hydride 203 K superconductor

## TL;DR

This study investigates the superconducting properties of sulfur hydride at 203 K, revealing its London penetration depth, energy gap, and fluctuation temperature scale, and concludes that its three-dimensional nature minimizes fluctuation effects on its critical temperature.

## Contribution

The paper provides the first detailed measurements of key superconducting parameters in sulfur hydride at 203 K and highlights the role of three-dimensionality in reducing fluctuation effects.

## Key findings

- London penetration depth is 189 nm.
- Superconducting energy gap is 27.8 meV.
- Fluctuation temperature scale is 1470 K, indicating fluctuations do not limit Tc.

## Abstract

Recently, compressed H$_2$S has been shown to become superconducting at 203 K under a pressure of 155 GPa. One might expect fluctuations to dominate at such temperatures. Using the magnetisation critical current, we determine the ground-state London penetration depth, $\lambda_0$=189 nm, and the superconducting energy gap, $\Delta_0$=27.8 meV, and find these parameters are similar to those of cuprate superconductors. We also determine the fluctuation temperature scale, $T_{\textrm{fluc}}=1470$ K, which shows that, unlike the cuprates, $T_c$ of the hydride is not limited by fluctuations. This is due to its three dimensionality and suggests the search for better superconductors should refocus on three-dimensional systems where the inevitable thermal fluctuations are less likely to reduce the observed $T_c$.