Condensed Matter Seminar | Helen Bouchiat, U of Paris Sud | "Revealing the second-order topological character of bismuth-based Josephson junction" | Joseph Henry Room

Wed, Feb 19, 2020, 12:00 pm
Joseph Henry Room

 In Second-Order Topological Insulators (SOTI), bulk and surfaces are insulating while the edges or hinges conduct current in a quasi-ideal (ballistic) way, being insensitive to disorder.  Crystalline bismuth has been shown to belong to this class of materials [1,2,3]. Just like the case of Quantum Spin Hall edges of 2D Topological Insulators, current is expected to be carried without dissipation by counter-propagating ballistic helical states, with a spin orientation locked to the momentum. Such edge or hinge states open many possibilities, from dissipationless charge and spin transport to new avenues for quantum computing.   We have investigated Crystalline Bi nanowires based Josephson junctions and found that they exhibit saw-tooth current phase relations robust in high magnetic field which is the signature one-dimensional ballistic edge states.  We also demonstrate the topological nature of Andreev states  in these junctions  when coupled to a microwave resonator in a  phase-biased configuration.   We find absorption peaks at the Andreev level crossings, whose temperature and frequency dependencies point to  protected topological  crossings  with an accuracy limited by the electronic temperature of our experiment.