IQIM Postdoctoral and Graduate Student Seminar

Abstract: In this talk, we discuss proximitized gate-defined germanium hole nanowires as a potential platform for Majorana zero modes. We present theoretical topological phase diagrams for different wire geometries as well as estimates for the size of the topological gap in dependence on various system parameters, based on which we critically discuss under which conditions Ge hole nanowires may manifest Majorana zero modes. While we generally find that the pristine topological gaps are smaller than in InAs-based devices, the main advantage of the Ge-based platform is the extremely high quality of current state-of-the-art Ge quantum wells (hole mobilities exceeding one million, mean-free paths on the order of tens of microns). By numerically calculating the local tunneling conductance spectra in the topological phase for realistic disorder strengths, we show that the high material quality leads to a significant reduction of spurious signals stemming from disorder-induced in-gap Andreev bound states, and, therefore, to less ambiguity in the experimental transport data compared to what is reported in InAs- or InSb-based devices, where the presence of substantial disorder is likely the most challenging obstacle for future progress. Finally, if time permits, we will additionally discuss planar Josephson junctions based on two-dimensional Ge hole gases as an alternative platform for Ge-based Majorana zero modes.

Lunch will be provided, following the talk, on the lawn north of the Bridge Building.