Flux-induced topological superconductivity in full-shell nanowires

Abstract

We present a novel route to realizing topological superconductivity using magnetic flux applied to a full superconducting shell surrounding a semiconducting nanowire core. In the destructive Little-Parks regime, reentrant regions of superconductivity are associated with integer number of phase windings in the shell. Tunneling into the core reveals a hard induced gap near zero applied flux, corresponding to zero phase winding, and a gapped region with a discrete zero-energy state around one applied flux quantum, Φ0 = h/2e, corresponding to 2π phase winding. Theoretical analysis indicates that in the presence of radial spin-orbit coupling in the semiconductor, the winding of the superconducting phase can induce a transition to a topological phase supporting Majorana zero modes. Realistic modeling shows a topological phase persisting over a wide range of parameters, and reproduces experimental tunneling conductance data. Further measurements of Coulomb blockade peak spacing around one flux quantum in full-shell nanowire islands shows exponentially decreasing deviation from 1e periodicity with device length, consistent with Majorana modes at the ends of the nanowire. arXiv:2003.13177v1 [cond-mat.mes-hall]

Nonlocal Conductance Spectroscopy of Andreev Bound States: Symmetry Relations and BCS Charges

“…Tunneling spectroscopy is a well-established tool for studying normal metal-superconductor (NS) hybrid systems. In the context of topological superconductors, tunneling spectroscopy is widely used in attempts to identify Majorana bound states (MBSs) [1][2][3][4][5][6][7], the prediction being that a single isolated Majorana mode should yield a zero-bias peak that is quantized to a conductance of 2e 2 /h for temperatures much below the scale of the tunneling broadening [8][9][10]. For overlapping Majorana states, the overlap gives distinct features in the two-probe conductance [10,11] which become very pronounced when probed with a quantum dot [4,[12][13][14][15].…”

“…With the limitations of such a two-probe measurement, it is natural to investigate other types of finite-bias spectroscopy to access the nonlocal properties of the subgap states. One approach is to use Coulomb-blockaded Majorana islands, where two normal probes are connected to the ends of the island and the proximitizing superconductor is floating [7,[21][22][23][24][25]. Linear-response sequential transport is then possible only through states that have support at both ends of the island.…”

Anomalous metallic phase in tunable destructive superconductors

“…1(a). Subsequent fabrication used standard electronbeam lithography, deposition, etching, and liftoff, as described elsewhere [27]. Devices were operated in two configurations [ Fig.…”

“…1(b)]: In the first configuration, four Au contacts were made to the Al shell allowing four-wire resistance measurements; In the second, an additional tunneling contact to the InAs core at the end of the wire was used as a tunnel probe, giving local density of states, as discussed in Ref. [27]. We investigated wires from three growth batches, denoted A, B, and C, with different core diameters, d C , and shell thicknesses, t S (see Supplementary Methods).…”

Number-conserving analysis of measurement-based braiding with Majorana zero modes

“…There has been impressive experimental progress in tuning semiconductor-superconductor nanowires into a topological superconducting phase hosting MZMs at either endpoint. [9][10][11][12][13][14][15][16][17][18][19][20] The continued experimental improvement of these systems has led to theoretical interest in designing Majoranabased qubits out of such heterostructures. [21][22][23][24][25] In particular, several works in the last few years have proposed chargeprotected Majorana-based qubits.…”