MaGnum · Majorana bound states in Ge/SiGe heterostructures

Each particle has its antiparticle, and upon bringing them in close vicinity, they annihilate (they disappear). A fundamental question arises: what happens if a particle is its own antiparticle? Ettore Majorana predicted their existence and evidence has been put forward for the existence of such a state of matter in the form of quasiparticle excitations in hybrid semiconductor-superconductor devices. Research activites so far has concentrated on InAs nanowires, planar InAs and InSb nanowires. Theory suggests to look for Majorana bound states (MBS) in Germanium and I propose to use a novel yet promising material system, namely a Germanium/Silicon-Germanium heterostructure, to provide evidence for the topological state of matter leading to Majorana bound states (MBS). Using Ge/SiGe brings the advantage of a long mean free path, which will allow for a larger spatial separation of the MBS and facilitate the long anticipated but yet elusive detection of correlation of two MBS. Additionally, the planar geometry brings the possibility to couple the MBS to their environment, which will be important for their usage as topologically protected quantum bits for quantum computation. I propose to show step-by-step the ingredients necessary for a topological phase transition resulting in MBS. In particular, I will follow these steps: I will collaborate with G. Isella's group to develop a highly mobile two-dimensional hole gas and make it accessible for magneto-transport measurements. I will further confine the holes into a one-dimensional wire with tunable tunneling barriers at each end. I will test the presence of a strong spin-orbit interaction by measuring helical transport. I will induce superconducting order by coupling the wire to NbTiN contacts. Finally, I will test the presence of MBS with tunneling conductance measurements and use a proper geometry to show evidence of the correlation of two MBS at each end of the wire.