Proximity effect in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ and La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ bilayers on SrTiO$_{3}$(110)

Long-range proximity effect has been reported in heterostructures of ferromagnetic half-metal La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ (LCMO) and $d$-wave superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO), which tends to be explained in terms of an induced spin-triplet state at the interfaces. However, in most of the theoretical models the interface is often normal to CuO$_{2}$ planes, whereas in most of the experiments transport properties along $c$-axis are studied. Bilayers of YBCO (20 nm) and LCMO (20 nm) were prepared by PLD technique on (110) oriented substrates, with the bottom layer either LCMO or YBCO. \textit{In situ} RHEED observations reveal that in the former the interface between LCMO and YBCO is flat. Accordingly superconductivity is completely suppressed due to the effective injection of spin-polarized electrons along the nodal direction. Whereas in the later the interface is rather rough so that superconductivity survives, although Tc is reduced and a very large transition width manifests. It was therefore suspected that in the later there exists a thin layer of LCMO at the interface with spin nonlinear configuration, which causes spin-flip leading to the triplet pairing. We nevertheless recognized a positive magnetoresistance at the vicinity of Tc in either an in-plane or an out-of-plane magnetic field. It is noted Hc$_{2}$ is remarkably higher either along the [1-10] or the [001] direction, when the field is along the CuO$_{2}$ plane and normal to the interface. This is, however, still compatible with the ordinary behavior of YBCO, although an anomaly in the anisotropic ratio is noticed.