Long range proximity effect in La2/3Ca1/3MnO3 (LCMO)/(100)YBa2Cu3O7-delta (YBCO) ferromagnet/superconductor bilayers: Evidence for induced triplet superconductivity in the ferromagnet

摘要

Scanning tunneling spectroscopy measurements conducted on epitaxially grownbilayers of half-metallic ferromagnetic La2/3Ca1/3MnO3 (LCMO) onsuperconducting (SC) (100)YBa2Cu3O7-delta (YBCO) reveal long-range penetrationof superconducting order into the LCMO. This anomalous proximity effectmanifests itself in the tunneling spectra measured on the LCMO layer as gapsand zero bias conductance peaks. Remarkably, these proximity-induced spectralfeatures were observed for bilayers with LCMO thickness of up to 30 nm, anorder of magnitude larger than the expected ferromagnetic coherence length inLCMO. We argue that this long-range proximity effect can be accounted for bythe formation of spin triplet pairing at the LCMO side of the bilayer due tomagnetic inhomogeneity at the interface or at domain walls. Possible symmetriesof the induced order parameter are discussed.