Order parameter oscillations in Fe/Ag/Bi₂Sr₂CaCu₂O_8+δ tunnel junctions

We have performed temperature-dependent tunneling conductance spectroscopy on Fe/Ag/Bi₂Sr₂CaCu₂O_8+δ (BSCCO) planar junctions. The multilayered Fe counterelectrode was designed to probe the proximity region of the ab plane of BSCCO. The spectra manifested a coherent oscillatory behavior with magnitude and sign dependent on the energy, decaying with increasing distance from the junction barrier, in conjunction with the theoretical predictions involving d-wave superconductors coupled with ferromagnets. The conductance oscillates in antiphase at E=0 and E=±Δ. The zero-bias conductance peak behavior is explained by a spin-dependent energy shift and the presence of a broken time-reversal pairing symmetry, which do not depend on the geometrical characteristics of the ferromagnetic film.