# Time-reversal symmetry breaking in the noncentrosymmetric Zr$_3$Ir superconductor

## TL;DR

This paper reports the discovery of Zr3Ir as an unconventional noncentrosymmetric superconductor that breaks time-reversal symmetry, characterized by muon-spin rotation/relaxation techniques and supported by electronic structure calculations.

## Contribution

It introduces Zr3Ir as a new noncentrosymmetric superconductor with broken time-reversal symmetry, combining experimental and theoretical analysis.

## Key findings

- Zr3Ir has a superconducting transition temperature of 2.3 K.
- Muon experiments reveal spontaneous magnetic fields below Tc.
- Superfluid density indicates a fully-gapped superconducting state.

## Abstract

We report the discovery of Zr$_3$Ir as a new type of unconventional noncentrosymmetric superconductor (with $T_c = 2.3$ K), here investigated mostly via muon-spin rotation/relaxation ($\mu$SR) techniques. Its superconductivity was characterized using magnetic susceptibility, electrical resistivity, and heat capacity measurements. The low-temperature superfluid density, determined via transverse-field $\mu$SR and electronic specific heat, suggests a fully-gapped superconducting state. The spontaneous magnetic fields, revealed by zero-field $\mu$SR below $T_c$, indicate the breaking of time-reversal symmetry in Zr$_3$Ir and, hence, the unconventional nature of its superconductivity. By using symmetry arguments and electronic-structure calculations we obtain a superconducting order parameter that is fully compatible with the experimental observations. Hence, our results clearly suggest that Zr$_3$Ir represents a new member of noncentrosymmetric superconductors with broken time-reversal symmetry.