Possible spin-triplet superconducting phase in the La_(0.7)Sr_(0.3)MnO_3/YBa_2Cu_3O_7/La_(0.7)Sr_(0.3)MnO_3 trilayer

摘要

We report on results of conductance spectroscopy measurements in the current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries ([001] and [100] directions respectively) of La_(0.7)Sr_(0.3)MnO_3/ YBa_2Cu_3O_7/La_(0.7)Sr_(0.3)MnO_3 (LSMO/YBCO/LSMO) nonsymmetric trilayer structures in order to search for signature of the formation of spin-triplet phase. This trilayer shows an enhancement of the superconducting transition temperature in magnetic field parallel to the plane. We argue that this enhancement is a result of the formation of spin-triplet phase. The differential conductance (dI/dV) spectra show fully developed zero-bias conductance peaks (ZBCP). The ZBCP measured in CIP geometry demonstrates a sharp shape. This could be attributed to a spin-triplet state arising from the proximity effect at the interface of the half-metal with the d-wave superconductor, similar as was predicted theoretically for the p-wave superconductor and observed experimentally in p-wave Sr_2RuO_4 superconductor. The measurements of the dI/dV in CPP geometry reveal a V shape similar as was experimentally observed in YBCO superconductor and predicted theoretically for superconductor with a d_(x~2-y~2) pairing symmetry of the order parameter.