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

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 ($\hat{I}¼$SR) techniques. Its superconductivity was characterized using magnetic susceptibility, electrical resistivity, and heat capacity measurements. The low-temperature superfluid density, determined via transverse-field $\hat{I}¼$SR and electronic specific heat, suggests a fully-gapped superconducting state. The spontaneous magnetic fields, revealed by zero-field $\hat{I}¼$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.

6 pages, 4 figuress; supplementary materials can be accessed from corresponding authors