Christian Koch



MMRES student at ICN2
Class 2019-2020

After MMRES:

PhD at ICN2

Study of hybrid crystal nanostructures for topological quantum computing


Hybrid crystal nanostructures that combine three types of materials – a III-V semiconductor, a ferromagnetic insulator and a superconductor – constitute the physical platform for a type of quasiparticle called Majorana Zero Modes (MZM). MZM are promising candidates for potential applications in highly scalable and stable topological quantum computing. The undesired destruction of topological MZM states, caused by imperfections in the interface coupling between the different crystalline materials during the epitaxial growing process, remains as an obstacle to be surpassed.

In this work, we examine the crystalline structures and elemental distribution in the nanomaterials of interest at the atomic scale, by means of Transmission Electron Microscopy imaging and spectroscopy techniques. We correlate our observations of remarkable features in the materials with their growing process to assess their viability as potential hosts for MZM. Specifically, we analyze various material combinations involving III-V semiconductors, such as indium arsenide (InAs), the ferromagnetic insulator europium (II) sulfide (EuS) and low temperature superconductors, such as aluminum (Al).

We show domain-based epitaxial growth in polycrystalline form, due to energetically equivalent crystal orientations, of Al on InAs substrates. We report on the formation of misfit dislocations allowing for the partial plastic relaxation of EuS grown on top of III-V semiconductor substrates and, in the case of III-V semiconductor nanowires with superconductor deposition, we discuss the diffusion of the superconductor throughout the nanowire. These findings will set the ground for the further optimization of hybrid crystal growing processes for topological quantum computing systems.

Major project supervisor

Jordi Arbiol

Minor project supervisor

Víctor F. Puntes, Neus Gómez Bastus