Contact Andreev Reflection Research Articles

Andreev reflection study of the new magnetic superconductor Mo3Sb7 in magnetic field

Andreev reflection in contacts based on the magnetic superconductor Mo3Sb7 in a magnetic field is investigated by the point-contact method. It is found that the behavior of the order parameter in the magnetic field Δ(H) is essentially dependent on the value of Δ, which varies widely (Δ(0,0)≈0.01–0.31meV) for different contacts at practically invariant Tc. At high Δ the dependence Δmax(H) deviates slightly from the theoretical prediction applicable under point-contact conditions. As the order parameter decreases, the deviation starts to increase and becomes very large when Δ approaches its minimum. Proceeding from the results obtained in this study and from the temperature measurements on Mo3Sb7 performed previously, we are inclined as before to assign the compound to the class of superconductors with an anisotropic gap function. Therefore, in no way can it be considered as a conventional BCS-type superconductor. The upper critical field Hc2≃16.5kOe found here is close to that obtained from magnetization measurements in other studies. According to an estimate made, the pair-breaking effect of the Pauli paramagnetism is rather weak in Mo3Sb7.

Andreev spectroscopy of point contacts between a low-temperature superconductor and manganite

Andreev reflection in contacts between a low-temperature superconductor (Pb or MgB2) and the manganite La0.65Ca0.35MnO3 (LCMO) is investigated. In the majority of cases behavior typical of superconductor/half-metallic ferromagnet contacts is observed: an excess voltage Vexc and suppression of the contact conductance G(V)=dI(V)∕dV in the region of voltages e∣V∣≤ΔS, where ΔS is the energy gap of the injector. However, some of the contacts demonstrate an increase of the conductance and an excess current Iexc on the current–voltage characteristic of the contact at e∣V∣≤ΔS. The character of the dI(V)∕dV curves observed for those contacts corresponds to Andreev spectrum of a superconductor with an energy gap much larger than the injector gap ΔS. It is assumed that in contacts of the latter type, specific conditions prevail whereby the penetration of Cooper pairs into the manganite from an electrode with a singlet order parameter induces in the surface region of the manganite a superconducting state with a triplet type of correlations.

Andreev Conductance of a ferromagnet-superconductor point contact

Based on the boundary conditions derived for quasiclassical Green’s functions, a theory of Andreev reflection in ferromagnet-superconductor point contacts is constructed. From a comparison with experimental data, the polarization of the conduction band was estimated for a number of ferromagnetic materials used in experiments on Andreev spectroscopy.

Conduction across the interface between a superconductor and a spin polarized metal

We have studied Andreev reflection in point contacts formed between several low T/sub c/ superconductors and various spin polarized normal metals. We have also developed a theoretical model for the phenomenon. There is good accordance between theory and experiment.