Unconventional superconductivity in Cr-based nitride La ₃ Cr _{10– <i>x</i>} N ₁₁

Abstract Magnetization, specific heat, and muon spin relaxation (μSR) experiments have been carried out on the Cr-based nitride superconductor La 3 Cr 10− x N 11 , which exhibits a number of unconventional superconducting properties. The susceptibility χ ( T ) shows nearly perfect superconducting diamagnetism (4 π χ ( T = 0) ≈ −1) and a remarkably high upper critical field μ 0 H c2 = 11.2 T. The specific heat displays activated exponential behavior exp(− Δ 0 / k B T ), together with a large and field-dependent residual Sommerfeld coefficient. Transverse-field muon spin relaxation (μSR) measurements suggest s+s-wave or p-wave pairing symmetry, ruling out single s-wave pairing. Zero-field μSR yields no statistically significant evidence for time reversal symmetry breaking (TRSB), and places an upper bound of 1.5(1.3) ms −1 on any TRSB-induced muon relaxation rate at T = 0. Our results suggest that the unconventional superconductivity in Ln 3 Cr 10– x N 11 , Ln = La and Pr, is mainly due to Cr 3d electrons and is similar in both compounds, whereas Pr 4f electrons are primarily responsible for the TRSB superconductivity observed in Pr 3 Cr 10− x N 11 .