Andreev-reflection spectroscopy with superconducting indium - a case study
Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FIN-20014 Turku, Finland Turku University Centre for Materials and Surfaces (MatSurf), FIN-20014 Turku, Finland
Wihuri Physical Laboratory, Department of Physics and Astronomy, University of Turku, FIN-20014 Turku, Finland
The National Doctoral Programme in Nanoscience (NGS-NANO), FIN-40014 University of Jyväskylä, Finland
Received October 29, 2012
We have investigated Andreev reflection at interfaces between superconducting indium (Tc = 3.4 K) and several normal conducting nonmagnetic metals (palladium, platinum, and silver) down to T = 0.1 K as well as zinc (Tc = 0.87 K) in its normal state at T = 2.5 K. We analyzed the point-contact spectra with the modified onedimensional BTK theory valid for ballistic transport. It includes Dynes’ quasiparticle lifetime as fitting parameter Γ in addition to superconducting energy gap 2Δ and strength Z of the interface barrier. For contact areas from less than 1 nm2 to 10000 nm2 the BTK Z-parameter was close to 0.5, corresponding to transmission coefficients of about
80%, independent of the normal metal. The very small variation of Z indicates that the interfaces have a negligible dielectric tunneling barrier. Also Fermi surface mismatch does not account for the observed Z. The extracted value Z ≈ 0.5 can be explained by assuming that practically all of our point contacts are in the diffusive regime.
PACS: 85.30.Hi Surface barrier, boundary, and point contact devices; PACS: 73.40.–c Electronic transport in interface structures; PACS: 74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions.
Key words: point contacts, metal interfaces, normal reflection, Andreev reflection.