Time-reversal symmetry breaking in the noncentrosymmetric Zr3Ir superconductor

Abstract

We report the discovery of Zr 3 Ir as a structurally different type of unconventional noncentrosymmetric superconductor (with T c = 2.3 K), here investigated mostly via muon-spin rotation/relaxation (μSR) techniques. Its superconductivity was characterized using magnetic susceptibility, electrical resistivity, and heat capacity measurements. The low-temperature superfluid density, determined via transverse-field μSR and electronic specific heat, suggests a fully gapped superconducting state. The spontaneous magnetic fields, revealed by zero-field μSR 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 structurally different member of noncentrosymmetric superconductors with broken time-reversal symmetry.

Multigap superconductivity in centrosymmetric and noncentrosymmetric rhenium-boron superconductors

“…More interestingly, by using the muon-spin relaxation (μSR) technique, time-reversal symmetry (TRS) breaking has been observed to occur in the superconducting state of selected weakly correlated NC-SCs. These include CaPtAs [17], LaNiC 2 [19], La 7 T 3 (T = transition metal) [20][21][22], Zr 3 Ir [23], and ReT [24][25][26][27]. Except for CaPtAs, where TRS breaking and superconducting gap nodes coexist below T c [17,28], in most other cases the superconducting properties resemble those of conventional superconductors, characterized by a fully opened energy gap.…”

Time-Reversal Symmetry Breaking in Re-Based Superconductors: Recent Developments

“…Surprisingly, the superconducting properties of the latter largely resemble those of conventional superconductors, i.e., their properties are clearly distinct from those of the above mentioned strongly-correlated NCSCs. To date, only a handful of NCSC families have been shown to exhibit TRS breaking in the superconducting state, including LaNiC 2 [14], La 7 (Rh,Ir) 3 [15,21], Zr 3 Ir [22], CaPtAs [16], and ReT [14][15][16][17][18][19][20]. Except for the recently studied CaPtAs, where coexisting TRS breaking and superconducting gap nodes were observed below T c , in most of the above cases the superconducting properties evidence a conventional s-wave pairing, characterized by a fully opened superconducting gap.…”

Intrinsic Nature of Spontaneous Magnetic Fields in Superconductors with Time-Reversal Symmetry Breaking

“…There is currently no accepted theory which predicts how large the spontaneous field should be, to what extent these spontaneous fields should be screened by supercurrents, whether these fields are particularly associated with defects, interfaces and domain boundaries, or indeed whether the presence of the muon itself might play the role of a defect. Nevertheless, the results of µSR experiments have been used to argue for TRSB on the basis of spontaneous fields detected in a number of unconventional superconductors, including Sr 2 RuO 4 [5], LaNiC 2 [21], SrPtAs [22], Zr 3 Ir [23,24], Re [25], and Re 6 Zr [26]. In this Letter, we critically reexamine these experiments by calculating the muon site in these candidate TRSB superconductors using density functional theory (DFT), to assess the degree to which the muon perturbs its local environment.…”