Andreev bound states in normal and ferromagnet/high-Tc superconducting tunnel junctions

TL;DR

This study experimentally investigates how exchange potential influences spin-polarized currents and Andreev bound states in tunnel junctions involving high-Tc superconductors, revealing effects of spin filtering and broken time reversal symmetry.

Contribution

It provides new experimental insights into the impact of exchange potential and spin polarization on Andreev bound states in high-Tc superconductor junctions.

Findings

Zero bias conductance peak splits into symmetric peaks with normal counterelectrode.

Asymmetric peaks observed with ferromagnetic layer due to spin filtering.

Conductance at zero energy aligns with recent theoretical predictions.

Abstract

Ag/BSCCO and Fe/Ag/BSCCO planar tunnel junctions were constructed in order to study experimentally the effect of an exchange potential on the spin polarized current transported through Andreev bound states appearing at the interface with a superconductor with broken time reversal pairing symmetry. The zero bias conductance peak (ZBCP) resulting from the Andreev bound states (ABS) is split into two symmetric peaks shifted at finite energies when the counterlectrode is normal. Four asymmetric peaks are observed when the ferromagnetic spin polarized charge reservoir is added, due to the combined effect of a spin-filtering exchange energy in the barrier, which is a spin dependent phenomenon, and the spin independent effect of a broken time reversal symmetry (BTRS). The polarization in the iron layer leads to asymmetry. Due to the shift of ABS peaks to finite energies, the conductance at zero energy behaves as predicted by recent theoretical developments for pure d-wave junctions without Andreev reflections.