Evaluation of spin polarization inp-In0.96Mn0.04As using Andreev reflection spectroscopy including inverse proximity effect

Abstract

We report on carrier transport across a superconductor/ferromagnetic semiconductor junction with a highly transparent metallic contact, Nb/$p$-In${}_{0.96}$Mn${}_{0.04}$As. Below $~$10 K, $p$-In${}_{0.96}$Mn${}_{0.04}$As becomes ferromagnetic, as evidenced by the hysteretic transverse resistance caused by the anomalous Hall effect. Below the superconducting critical temperature $T$${}_{c}$ of the Nb electrodes (8.2 K), a conductance reduction occurs within the bias voltage that is comparable to the Nb superconducting energy gap. A rather moderate slope in the differential conductance curves within the gap region indicates the partial suppression of the Andreev reflection caused by spin-polarized carriers in $p$-In${}_{0.96}$Mn${}_{0.04}$As. Spin polarization $P$ in $p$-In${}_{0.96}$Mn${}_{0.04}$As has been extracted by fitting the measured differential conductance curves with a newly modified Blonder-Tinkham-Klapwijk model with both spin polarization and the inverse proximity effect (mod2-BTK model). The extracted $P$ value is $P$ $=$ 0.725 at 0.5 K, and it decreases gradually with increasing temperature.