Temperature dependence of differential conductance in Co-based Heusler alloy Co 2 TiSn and superconductor Pb junctions

Abstract We investigated temperature dependence of differential conductance G ( V ) in planar junctions consisting of Co-based Heusler alloy Co 2 TiSn and superconductor Pb. Ferromagnetic Co 2 TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co 2 TiSn 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 Δ 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 Δ ( 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 Co 2 TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co 2 TiSn/Pb interface.