# Superconductivity and the upper critical field in the chiral noncentrosymmetric superconductor NbRh$_{2}$B$_{2}$

## TL;DR

This study investigates the superconducting properties of NbRh₂B₂, revealing an unusually high upper critical field, multigap s-wave superconductivity, and deviations from traditional models, indicating complex superconducting behavior.

## Contribution

It provides the first detailed analysis of the superconducting gap structure and critical fields in NbRh₂B₂, highlighting its multigap nature and exceeding the Pauli limit.

## Key findings

- Upper critical field exceeds Pauli limit (~18 T vs. 13.9 T)
- Superconducting gap is multigap s+s-wave
- Pressure dependence indicates s-wave superconductivity

## Abstract

NbRh$_{2}$B$_{2}$ crystallises in a chiral noncentrosymmetric structure and exhibits bulk type-II superconductivity below $7.46(5)$~K. Here we show that the temperature dependence of the upper critical field deviates from the behaviour expected for both Werthamer-Helfand-Hohenberg and the Ginzburg-Landau models and that $\mu_{0}H_{\mathrm{c2}}\left(0\right)\approx 18$~T exceeds the Pauli paramagnetic limit, $\mu_{0}H_{\mathrm{P}}=13.9$~T. We explore the reasons for this enhancement. Transverse-field muon spectroscopy measurements suggest that the superconducting gap is either $s$-wave or $\left(s+s\right)$-wave, and the pressure dependence of $T_{\mathrm{c}}$ reveals the superconducting gap is primarily $s$-wave in character. The magnetic penetration depth $\lambda(0) = 595(5)$~nm. Heat capacity measurements reveal the presence of a multigap $\left(s+s\right)$-wave superconducting order parameter and moderate electron-phonon coupling.