Evidence for triplet superconductivity near an antiferromagnetic instability in CrAs*

Unconventional superconductivity, where the Cooper pairs are bound by a mechanism other than the conventional electron-phonon pairing mechanism described by BCS theory, has often been found to occur in close proximity to magnetic order in systems such as the cuprates, iron pnictides and heavy fermion superconductors. Recently CrAs has been discovered to show superconductivity as the helimagnetic order is suppressed by applying pressure[1], suggesting possible unconventional superconductivity. To reveal the nature of the superconducting order parameter of CrAs, we performed measurements of the angular dependence of upper critical field(B_c2) of CrAs under pressure using a triple-axis vector magnet. We find a clear anisotropy of B_c2 in the bc plane, where both two-fold and six-fold oscillatory components are observed, which are consistent with an unconventional odd-parity triplet superconducting state[2].

[1] W. Wu et al., Nat. Commun. 5, 5508 (2014).
[2] C. Y. Guo et al., arXiv: 1710. 06707 (2017).