Masters Defense: Aske Gejl
Investigating InAsSb Nanowires for Majorana Fermion Devices
In recent years Majorana fermions have been identified as a possible platform for per- forming fault-tolerant quantum information processing due to their non-abelian ex- change statistics and topological protection against decoherence. In hybrid nanowire/ superconductor systems Majorana fermions are proposed to emerge as quasiparticle excitations, Majorana zero modes. This thesis concerns measurements on Majorana zero mode devices on InAsSb/Al hybrid nanowires. One of the prerequisites for the emergence of Majorana zero modes in hybrid nanowire/superconductor systems is a large spin-splitting. Recent theory predicts InAsSb nanowires to exhibit signifi- cantly larger spin-splitting compared to InAs or InSb, in which transport signatures of Majorana zero modes have previously been reported. Here, we present transport measurements for two different types of InAs1−xSbxnanowires with molar fractions of x = 0.35 and x = 0.8. The study into the InAs0.65Sb0.35 nanowires is unique as they are in the wurtzite crystal structure, a crystal structure not previously reported for InAsSb. We find that the wurtzite crystal structure has a lower electron affinity than regular zinc-blende InAsSb nanowires, i.e. the wurtzite nanowires exhibit are more responsive to electrostatic gate potentials. The gateability may be crucial for the properties of future InAsSb devices. By using Coulomb and tunneling spec- troscopy transport signatures associated with Majorana zero modes are detected in two different device geometries. This is the first report on Majorana zero modes in InAsSb nanowires.