Towards Majorana Bound States Induced by Ferromagnets in Nanowires

Majorana bound states are topological states predicated in condensed matter physics. These states obey non-Abelian statistics and are promising candidates for topological quantum computing. Hybrid superconductor-semiconductor nanowires are believed to be platforms for Majorana bound states and experimental signatures have been reported in the past ten years. Nevertheless, there is still no strong evidence confirming observation of these topological states since these signatures may be attributed to trivial states.

This thesis focuses on semiconductor nanowire devices with ferromagnets. We first discuss local magnetic field effect induced by ferromagnets. By numerical simulations, we demonstrate how to induce and manipulate Majorana bound states in a Majorana nanowire or T-junction with ferromagnets. Hybrid superconductor-semiconductor nanowire devices with ferromagnets are fabricated. In quantum transport measurements, we observe hysteretic supercurrents and zero-bias peaks of differential conductance in these devices. Additionally, we observe long zero-bias peaks at zero applied magnetic field but at finite local magnetic field generated by ferromagnets. Even though a zero-bias peak is a signature of Majorana bound states, trivial Andreev bound states may also explain above observations. Future experiments based on hybrid devices with ferromagnets may give us insight into Majorana bound states and their applications in topological quantum computing.