Magnetoanisotropic spin-triplet Andreev reflection in ferromagnet-Ising superconductor junctions

TL;DR

This paper theoretically investigates magnetoanisotropic spin-triplet Andreev reflection in ferromagnet-Ising superconductor junctions, revealing a $oldsymbol{ ext{ extpi}}$-periodic magnetoanisotropy and conditions for enhanced Andreev reflection.

Contribution

It introduces a comprehensive theoretical framework for understanding spin-triplet Andreev reflection in Ising superconductor junctions, highlighting $ ext{ extpi}$-periodic magnetoanisotropy and potential spintronic applications.

Findings

Strong magnetoanisotropic spin-triplet Andreev reflection with $ ext{ extpi}$ period.

Complete Andreev reflection at the superconductor gap energy.

Enhanced Andreev reflection at oblique incident angles.

Abstract

We theoretically study the electronic transport through a ferromagnet-Ising superconductor junction. A tight-binding Hamiltonian describing the Ising superconductor is presented. Then by combing the non-equilibrium Green's function method, the expressions of Andreev reflection coefficient and conductance are obtained. A strong magnetoanisotropic spin-triplet Andreev reflection is shown, and the magnetoanisotropic period is $\pi$ instead of $2\pi$ as in the conventional magnetoanisotropic system. We demonstrate a significant increase of the spin-triplet Andreev reflection for the single-band Ising superconductor. Furthermore, the dependence of the Andreev reflection on the incident energy and incident angle are also investigated. A complete Andreev reflection can occur when the incident energy is equal to the superconductor gap, regardless of the Fermi energy (spin polarization) of the ferromagnet. For the suitable oblique incidence, the spin-triplet Andreev reflection can be strongly enhanced. In addition, the conductance spectroscopies of both zero bias and finite bias are studied, and the influence of gate voltage, exchange energy, and spin-orbit coupling on the conductance spectroscopy are discussed in detail. The conductance reveals a strong magnetoanisotropy with period $\pi$ as the Andreev reflection coefficient. When the magnetization direction is parallel to the junction plane, a large conductance peak always emerges at the superconductor gap. This work offers a comprehensive and systematic study of the spin-triplet Andreev reflection, and has underlying application of $\pi$-periodic spin valve in spintronics.