Reversal of the Upper Critical Field Anisotropy and Spin-Locked Superconductivity in K2Cr3As3

Recently, superconductivity in K2Cr3As3 (Tc =6.1 K) was discovered. The crystalline lattice contains an array of weakly coupled, double well [(Cr3As3)2-]∞ linkages stretched along the c axis, suggesting the possibility of quasi-one-dimensional superconductivity. Moderately anisotropic upper critical field was revealed in single crystals, with very large initial slopes, dH∥c2 /dT=12 T/K along the Cr chains and dHperpendicularc2 /dT =7 T/K perpendicular to the chains. Given the ambiguity of conclusions based on the extrapolations of Hc2(T) measured near Tc to low temperatures, we performed high-field measurements of Hc2(T) on K2Cr3As3 single crystals in pulsed magnetic fields which enabled us to reveal the full anisotropic Hc2(T) curves from Tc down to 600 mK.