Andreev Reflection and Pair Breaking Effects at the Superconductor/Magnetic Semiconductor Interface

TL;DR

This study examines Andreev reflection at superconductor/magnetic semiconductor interfaces, revealing pair-breaking effects in ferromagnetic (Ga,Mn)As that influence conductance spectra and enable spin polarization measurement.

Contribution

It demonstrates that pair-breaking effects in (Ga,Mn)As affect Andreev reflection spectra and introduces a method to evaluate spin polarization in magnetic semiconductors.

Findings

Conventional Andreev reflection observed in non-magnetic (Ga,Be)As.

Conductance spectra in ferromagnetic (Ga,Mn)As show broadened density of states.

Estimated spin polarization in (Ga,Mn)As is 83+/-17%.

Abstract

We investigate the applicability of spin polarization measurements using Andreev reflection in a point contact geometry in heavily doped dilute magnetic semiconductors, such as (Ga,Mn)As. While we observe conventional Andreev reflection in non-magnetic (Ga,Be)As epilayers, our measurements indicate that in ferromagnetic (Ga,Mn)As epilayers with comparable hole concentration the conductance spectra can only be adequately described by a broadened density of states and a reduced superconducting gap. We suggest that these pair-breaking effects stem from inelastic scattering in the metallic impurity band of (Ga,Mn)As and can be explained by introducing a finite quasiparticle lifetime or a higher effective temperature. For (Ga,Mn)As with 8% Mn concentration and 140 K Curie temperature we evaluate the spin polarization to be 83+/-17%. PACS numbers: 72.25.Dc,72.25.Mk,74.45.+c