Unconventional superconductivity in Cr-based compound Pr₃Cr_10-xN₁₁

We report results of specific heat and muon spin relaxation (mu SR) measurements on a polycrystalline sample of Pr3Cr10-xN11, which shows superconducting state below T-c = 5.25 K, a large upper critical field H-c2 similar to 20 T and a residual Sommerfeld coefficient gamma(0). The field dependence of gamma(0)(H) resembles gamma of the U-based superconductors UTe2 and URhGe at low temperatures. The temperature-dependent superfluid density measured by transverse-field mu SR experiments is consistent with a p-wave pairing symmetry. ZF-mu SR experiment suggests a time-reversal symmetry broken superconducting transition, and temperature-independent spin fluctuations at low temperatures are revealed by LF-mu SR experiments. These results indicate that Pr3Cr10-xN11 is a candidate of p-wave superconductor which breaks time-reversal symmetry.