Magnetic field dependence of the proximity-induced triplet superconductivity at ferromagnet/superconductor interfaces

Abstract

Long-ranged superconductor proximity effects recently found in superconductor-ferromagnetic (S-F) systems are generally attributed to the formation of triplet-pairing correlations due to various forms of magnetic inhomogeneities at the S-F interface. In order to investigate this conjecture within a single F layer coupled to a superconductor, we performed scanning tunneling spectroscopy on bilayers of La${}_{2/3}$Ca${}_{1/3}$MnO${}_{3}$ (LCMO) ferromagnetic thin films grown on high-temperature superconducting films of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ or Pr${}_{1.85}$Ce${}_{0.15}$CuO${}_{4}$ under various magnetic fields. We find a strong correlation between the magnitude of superconductor-related spectral features measured on the LCMO layer and the degree of magnetic inhomogeneity controlled by the external magnetic field. This corroborates theoretical predictions regarding the role played by magnetic inhomogeneities in inducing triplet pairing at S-F interfaces.