Point contact Andreev reflection from semimetallic bismuth—The roles of the minority carriers and the large spin-orbit coupling

Abstract

The Point Contact Andreev Reflection (PCAR) technique has been traditionally and predominantly applied to either the characterisation of superconductors or of spin-polarised metals. The sufficiently large and slowly varying, on the scale of tens of meV around the Fermi level (EF), Density of States (DOS) in metals and highly degenerate semiconductors significantly simplifies the interpretation and quantitative analysis of the measured Differential Conductance Spectra (DCS). Semimetals in general, and particularly the heavy semimetals, because of the presence of several carrier bands and the larger Spin-Orbit coupling, exhibit significantly higher variations in the DOS, close to EF, which can be observed and evaluated with PCAR. Here, DCS of bismuth/niobium point contacts are examined to reveal the relative energy offsets [0.12(3), 2.32(5), and 5.7(2)] meV and the approximate relative DOS contributions of the three main carrier bands (16:5:4). Apart from the bulk, some surface states are also expected to contribute to the observed DOS and be potentially spin-split. The spin polarisation due to all conducting states is evaluated at P≤ 0.09(7).