Tunneling Processes into Localized Subgap States in Superconductors

Abstract

We combine scanning-tunneling-spectroscopy experiments probing magnetic impurities on a superconducting surface with a theoretical analysis of the tunneling processes between (superconducting) tip and substrate. We show that the current through impurity-induced Shiba bound states is carried by single-electron tunneling at large tip-substrate distances and Andreev reflections at smaller distances. The single-electron current requires relaxation processes, allowing us to extract information on quasiparticle transitions and lifetimes.

Spin and charge signatures of topological superconductivity in Rashba nanowires

“…Two types of experiments could be carried out to detect the spin or charge reversal at the topological phase transition point. The first one is based on spin-polarized STM spectroscopy which allows one to inject a current in the lowest bands [32][33][34]47]. Depending on the polarization of the STM probe, a current will flow or not in the trivial phase and the opposite situation will occur in the topological phase.…”

“…Various candidate materials can host such topological states [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] but one of the most promising platforms are semiconducting nanowires of InAs or InSb material, with strong Rashba spin orbit interaction (SOI), subjected to an external magnetic field and in proximity to an s-wave superconductor [22,23]. Experimental evidence has been reported for topological phases in such wires [24][25][26][27][28][29][30][31] as well as in magnetic atomic chains on superconducting substrates [32][33][34]. However, most of the work so far has focused on the detection of the MFs in these nanowires and not on their bulk properties.…”

Magnetic manipulation of topological states in p-wave superconductors

“…Recently, there has been a tremendous effort in designing and realizing materials platforms where topological superconductivity and MFs can be successfully obtained. This is demonstrated by the proposal of a large variety of systems based on heterostructures made of topological insulators or semiconductors interfaced with s-wave superconductors (SCs) [6][7][8][9][10] as well as by the subsequent experimental evidence of MFs in hybrid superconducting devices [11][12][13][14][15][16][17][18][19][20].…”

Josephson effect in multiterminal topological junctions

“…Similar experiments have also been reported for other platforms, see for instance Refs. [14][15][16][17][18], and many of our results below apply to those implementations as well. It stands to reason that the currently developed technologies will give access to quantum transport studies in a wide variety of hybrid structures involving topological superconductor (TS) wires, including multiterminal geometries [12,13,19].…”