STAGE OFFRE DE STAGE : REVEALING TOPOLOGICAL EDGE STATES IN BISMUTH NANOWIRES BASED JOSEPHSON JUNCTIONS

We are exploring the type of superconductivity that can be induced in monocrystalline bismuth nanowires. In such nanowires, conduction is due to surface states that possess a huge spin orbit coupling energy, larger than the Fermi energy, a property that is rarely encountered. When these (non superconducting) nanowires are connected to superconducting contacts a supercurrent runs through them, called the “Josepshson current”. Our experiments found unexpected features of Josepshson effect attributed to the high spin-orbit interaction in the bismuth nanowires, that leads to the confinement of the supercurrent to very few 1D channels as predicted to occur at the edges of topological surfaces of the nanowires. We have recently provided a direct signature of ballistic 1D transport along these edge states. This was done by inserting the Bi nanowires in a SQUID interferometer, exploiting the extreme sensitivity of the relation between the Josephson current flowing through a nanostructure and the superconducting phase difference at its ends. The sharp sawtooth-shaped current-phase relation we find demonstrates that transport occurs ballistically along two edges of the nanowire, and confirms the predicted nearly perfect transmission of Cooper pairs through Quantum Spin Hall edge states. In addition, we showed the possibility to manipulate the phase of these supercurrent-carrying edge states and generate spin supercurrents.