Temperature dependence of differential conductance in Co-based Heusler alloy Co2TiSn and superconductor Pb junctions

We investigated temperature dependence of differential conductance G (V) in planar junctions consisting of Co-based Heusler alloy Co₂TiSn and superconductor Pb. Ferromagnetic Co₂TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co₂TiSn was deduced to be 60.0% at 1.4 K by the Andreev reflection spectroscopy. The G (V) spectral shape was smeared gradually with increasing temperature and its structure was disappeared above the superconducting transition temperature T_c. Theoretical model analysis revealed that the superconducting energy gap ∆ was 1.06 meV at 1.4 K and the T_c was 6.8 K , indicating that both values were suppressed from bulk values. However, the temperature dependent ∆ (T) behavior was in good agreement with that of the Bardeen-Cooper-Schrieffer (BCS) theory. The experimental results exhibit that the superconductivity of Pb attached to half-metallic Co₂TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co₂TiSn/Pb interface.