Millimeter Wave Study of Hybrid Superconducting Heterostructures with Magnetic Active Interlayer

We fabricated Nb/Au/(Ca_1-xSr_x)CuO₂/YBa₂Cu₃O₇ superconducting heterostructures with I_CRN product 100divide300 muV at T=4.2 K. Critical current density was 10 A/cm² through 50 nm thick Ca_1-xSr_xCuO₂ layer, and increased for thinner layers. Critical currents of the heterostructures had much smaller periods in l_c(H) dependencies compare to Josephson junctions without anti ferromagnetic layer. Half- integer Shapiro steps and detector responses were observed for the most of heterostructures. Current phase relations of the heterostructures deviated from sinusoidal with 10divide40% portion of the second harmonic.