Andreev Reflection and Pair Breaking Effects at the   Superconductor/Magnetic Semiconductor Interface
  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 
R.P. Panguluri, K.C. Ku, T. Wojtowicz, X. Liu, J.K. Furdyna, Y.B.   Lyanda-Geller, N. Samarth and B. Nadgorny