Spin-active interfaces and unconventional pairing in half-metal$\mid$superconductor junctions

TL;DR

This paper investigates how spin-active interfaces and unconventional pairing symmetries in half-metallic ferromagnet-superconductor junctions affect conductance, proximity effects, and local density of states, revealing the critical role of spin-dependent phase shifts.

Contribution

It provides a comprehensive analytical and numerical analysis of the influence of spin-active interfaces and unconventional pairing on physical properties of HM|S bilayers, highlighting the impact of spin-dependent phase shifts.

Findings

Spin-dependent phase shifts significantly alter conductance spectra.

Unconventional pairing symmetries induce surface-bound states sensitive to spin processes.

Results are experimentally testable via STM and point-contact spectroscopy.

Abstract

We study the physical properties of a half-metallic ferromagnet$\mid$superconductor (HM$\mid$S) bilayer, allowing for an arbitrary bulk pairing symmetry of the superconductor and spin-dependent processes at the interface. In particular, we study how the possibility of unconventional pairing such as $p$- and d-wave and a spin-active interface influence the \textit{(i)} conductance spectra, \textit{(ii)} proximity effect, and \textit{(iii)} local density of states of such a bilayer. Our calculation is done both analytically and numerically in the ballistic limit, using both a continuum- and lattice-model. It is found that the spin-dependent phase-shifts occuring at the HM$\mid$S interface seriously influence all of the aforementioned phenomena. We explain our results in terms of Andreev reflection in the presence of a spin-active interface, allowing for both spin-filtering and spin-mixing processes. We demonstrate how the surface-bound states induced by the anisotropy of the superconducting order parameter at the HM$\mid$S interface are highly sensitive to these spin-dependent processes. Our results can be directly tested experimentally using STM-measurements and/or point-contact spectroscopy.