Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor

TL;DR

This study provides experimental evidence that triplet superconducting correlations are induced in the superconductor side of a superconductor-ferromagnet interface, with tunneling spectra indicating changes in superconducting properties under magnetic fields.

Contribution

It demonstrates the presence of triplet-pairing correlations in the superconductor side of an S-F interface through tunneling spectroscopy measurements.

Findings

Anomalous gap structures observed at low magnetic fields

Spectra become more BCS-like at high magnetic saturation

Critical temperature of NbN increases with magnetic field

Abstract

Considerable evidence for proximity-induced triplet superconductivity on the ferromagnetic side of a superconductor-ferromagnet (S-F) interface now exists; however, the corresponding effect on the superconductor side has hardly been addressed. We have performed scanning tunneling spectroscopy measurements on NbN superconducting thin films proximity coupled to the half-metallic ferromagnet La2/3Ca1/3MnO3 (LCMO) as a function of magnetic field. We have found that at zero and low applied magnetic fields the tunneling spectra on NbN typically show an anomalous gap structure with suppressed coherence peaks and, in some cases, a zero-bias conductance peak. As the field increases to the magnetic saturation of LCMO where the magnetization is homogeneous, the spectra become more BCS-like and the critical temperature of the NbN increases, implying a reduced proximity effect. Our results therefore suggest that triplet-pairing correlations are also induced in the S side of an S-F bilayer.