Superconducting current and low-energy states in a mesa-heterostructure interlayered with a strontium iridate film with strong spin-orbit interaction

The superconducting current has been observed in mesa-heterostructures Nb/S r₂Ir O₄ /YB a₂C u₃O_x with a S r₂Ir O₄ interlayer having strong spin-orbit interaction. The superconducting critical current density j_C≈0.3 A /c m² for d =7 nm was registered at T =4.2 K . Magnetic-field dependence of superconducting critical current I_C(H ) showed a sharp central peak and minor oscillating behavior for sidelobes indicated the absence of pinholes. Integer and fractional Shapiro steps were observed at voltages V_{m ,n}=(m /n ) (h /2 e ) f_e under microwave radiation at frequencies f_e=38 GHz and f_e=50 GHz. Fractional Shapiro steps (m /n =1 /2 , 3/2) point on the presence of the second harmonic in the superconducting current-phase relation. The zero-bias conductance peak was observed hinting on existence of low-energy states at S r₂Ir O₄ /YB a₂C u₃O_x interface at temperatures higher than the superconducting critical temperature of Nb.