# Type-I superconductivity in noncentrosymmetric superconductor AuBe

## TL;DR

This study investigates the superconducting properties of AuBe, revealing it to be a weakly-coupled, fully gapped, type-I superconductor with preserved time-reversal symmetry, contrasting earlier reports of type-II behavior.

## Contribution

The paper provides the first evidence of type-I superconductivity in AuBe using muon-spin relaxation/rotation measurements, challenging previous findings of type-II superconductivity.

## Key findings

- AuBe has a superconducting transition at 3.2 K.
- AuBe exhibits type-I superconductivity with a Ginzburg-Landau parameter less than 1/√2.
- Time-reversal symmetry is preserved in AuBe's superconducting state.

## Abstract

The noncentrosymmetric superconductor AuBe have been investigated using the magnetization, resistivity, specific heat, and muon-spin relaxation/rotation measurements. AuBe crystallizes in the cubic FeSi-type B20 structure with superconducting transition temperature observed at $T_{c}$ = 3.2 $\pm$ 0.1 K. The low-temperature specific heat data, $C_{el}$(T), indicate a weakly-coupled fully gapped BCS superconductivity with an isotropic energy gap 2$\Delta(0)/k_{B}T_{c}$ = 3.76, which is close to the BCS value of 3.52. Interestingly, type-I superconductivity is inferred from the $\mu$SR measurements, which is in contrast with the earlier reports of type-II superconductivity in AuBe. The Ginzburg-Landau parameter is $\kappa_{GL}$ = 0.4 $<$ 1/$\sqrt{2}$. The transverse-field $\mu$SR data transformed in the maximum entropy spectra depicting the internal magnetic field probability distribution, P(H), also confirms the absence of the mixed state in AuBe. The thermodynamic critical field, $H_{c}$, calculated to be around 259 Oe. The zero-field $\mu$SR results indicate that time-reversal symmetry is preserved and supports a spin-singlet pairing in the superconducting ground state.