2e-periodic Switching Current Modulation in Nanowire Single Cooper Pair Transistors

Over the past years, many studies have reported on signatures of Majorana modes via zero-bias peaks. However, to date there have been no experiments demonstrating their non-Abelian statistics. Recently, Aasen et al. proposed that the Majorana fusion channels, intimately related to their non-Abelian statistics, could be probed in a single-wire geometry [1]. An outstanding issue for the fusion experiment, however, is quasiparticle poisoning, because it can lead to decoherence and readout errors.

Therefore, we studied parity effects in gate-tuneable single Cooper pair transistors made from proximitized InAs nanowires. We measured the gate modulation of the switching currents as a function of temperature, island length, and the magnetic field applied parallel to the wire. We observed 2e-periodic signals for a wide range of gate settings. This implies there are few deep quasiparticle traps present in the island. We develop a thermodynamic model, which shows that our island does experience rapid parity fluctuations despite this clean 2e signal. When increasing the magnetic field, an oscillating even-odd pattern appears. We attribute this to the zero-energy crossing of an Andreev bound state.

References:
[1] D. Aasen et al. PRX 6, 031016 (2016)