Periodic Reporting for period 2 - MajoranaTopIn (Majorana Fermions in Topological Insulator Platforms)
Reporting period: 2018-11-01 to 2020-04-30
On the fabrication technology front, we have optimized the technology to fabricate TI-based Josephson junction with Al as the superconducting (SC) electrode, and our devices present a record-high transparency at the TI/SC interface. In these Josephson-junction devices, we were able to tune the chemical potential of the TI surface states to the Dirac point by back gating and to demonstrate that a finite supercurrent is maintained even at the Dirac point, which is important for the future Majorana devices.
On the materials front, we have serendipitously discovered a novel route to realize a very good TI/SC interface; namely, we found that simply depositing Pd on the surface of (Bi,Sb)2Te3 thin film (which is a bulk-insulating TI material) leads to the epitaxial self-formation of superconducting PdTe2 layer through diffusion of Pd into (Bi,Sb)2Te3, and the resulting TI/SC interface shows almost a perfect transparency. This discovery will contribute significantly to the realization of TI-based superconducting devices to address Majorana fermions in the second half of this project.
There was also an important progress in the synthesis and device fabrications of TI nanowires. Specifically, we were able to directly elucidate the peculiar subband formation of the Dirac surface states due to quantum confinement in TI nanowires through gate-controlled transport experiments across the Dirac point. The realization of the subband structure peculiar to the topological surface states is an important prerequisite for using TI nanowires for the generation of Majorana fermions through the SC proximity effect, and hence its direct confirmation is of great importance.