Multigap superconductivity in chiral noncentrosymmetric TaRh2B2

Abstract

We report the observation of multigap superconductivity in TaRh 2 B 2 . We show TaRh 2 B 2 is a bulk type-II superconductor with a transition temperature T c = 6.00(5) K. We present transverse-field muon spin relaxation data where the superconducting gap can be fit using a two-gap (s + s)-wave model. We also report the zero-field electronic specific heat in the superconducting state that is best described by the same (s + s) model, providing further evidence of multiband behavior in this superconductor. Zero-field muon spin relaxation measurements show time-reversal symmetry is preserved in the superconducting state. We demonstrate that TaRh 2 B 2 has an upper critical field of 15.2(1) T, which is significantly higher than previously reported and exceeds the Pauli limit.

NbIr2B2 and TaIr2B2 – New Low Symmetry Noncentrosymmetric Superconductors with Strong Spin–Orbit Coupling

“…For example, multigap superconductivity, probed by the μSR technique, has been reported for isoelectronic but not isostructural TaRh 2 B 2 . [ 28 ]…”

“…For example, multigap superconductivity, probed by the μSR technique, has been reported for isoelectronic but not isostructural TaRh 2 B 2 . [28] The last experimental technique used for characterization of the new superconductors was temperature dependent resistivity with the results shown in the main panel of Figure 3d for NbIr 2 B 2 and Figure 3e for TaIr 2 B 2 . NbIr 2 B 2 behaves like a poor metal, with a shallow negative gradient for the resistivity upon cooling from room temperature.…”

Time-reversal symmetry breaking and multigap superconductivity in the noncentrosymmetric superconductor La7Ni3

“…This has a pronounced effect on the possible pairing states and leads to mixed-parity spin states (singlet and triplet) in the order parameter [4,[7][8][9]. As a result, it can give rise to some novel and uncommon superconducting properties, such as unusually high upper critical fields, larger than the Pauli limit [8,[10][11][12][13], the presence of nontrivial line or point nodes [14][15][16][17][18], multiple-gap behavior [12,19], an enhanced protection against impurity scattering [20][21][22][23][24][25][26][27], and the more recently proposed topological superconductivity [28][29][30][31][32][33].…”

Anisotropic superconductivity and unusually robust electronic critical field in single crystal La$_{7}$Ir$_{3}$

“…The lack of inversion symmetry in these materials means that parity is no longer a good quantum number and antisymmetric spin-orbit coupling can lead to an admixture of singlet and triplet Cooper pairs. While it is usual for one channel to dominate, such an admixture of singlet and triplet pairs may result in novel superconducting phenomena, including unusual superconducting gap structures [3][4][5], unconventional upper-critical field behavior [6], and time-reversal symmetry breaking (TRSB) [7][8][9][10][11][12][13][14][15][16][17].…”