Coexistence of a triplet nodal order-parameter and a singlet order-parameter at the interfaces of ferromagnet-superconductor Co/CoO/In junctions

TL;DR

This study investigates the coexistence of triplet and singlet superconducting order parameters at ferromagnet-superconductor interfaces, revealing mixed pairing states through conductance measurements and modeling.

Contribution

It demonstrates the simultaneous presence of s-wave singlet and p-wave triplet order parameters at Co/CoO/In junctions, supported by conductance data and theoretical fitting.

Findings

Conductance spectra show V-shaped low-bias features inconsistent with pure s-wave.

Both s-wave and p-wave gaps follow BCS temperature dependence.

The s-wave gap amplitude increases with barrier strength.

Abstract

We present differential conductance measurements of Cobalt / Cobalt-Oxide / Indium planar junctions, 500nm x 500nm in size. The junctions span a wide range of barriers, from very low to a tunnel barrier. The characteristic conductance of all the junctions show a V-shape structure at low bias instead of the U-shape characteristic of a s-wave order parameter. The bias of the conductance peaks is, for all junctions, larger than the gap of indium. Both properties exclude pure s-wave pairing. The data is well fitted by a model that assumes the coexistence of s-wave singlet and equal spin p-wave triplet fluids. We find that the values of the s-wave and p-wave gaps follow the BCS temperature dependance and that the amplitude of the s-wave fluid increases with the barrier strength.