Disorder-controlled superconductivity at YBa_(2)Cu_(3)O_(7)/SrTiO_(3) interfaces

We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa_(2)Cu_(3)O_(7) (YBCO) layers on SrTiO_(3) (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO_(2) and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO_(2) planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.