Induced superconductivity in topological edge states of 3D Dirac semimetal Bi_1-xSb_x

Bi has been identified as a higher-order topological insulator (HOTI). Following the same topology, without any band inversion, Bi_1-xSb_x (x=3%) reduces the gap at the L point enhancing the Dirac semimetal (DSM) nature of the bulk materials. We performed comprehensive study of proximity-induced supercurrent in Nb- Bi_1-xSb_x (x=3%)-Nb Josephson junctions fabricated on flakes of varying thickness and junction lengths. While we see a conventional Fraunhofer pattern in thinner flakes, for thicker flakes (~200 nm thickness) the critical current (Ic) modulates with magnetic field in a SQUID-like pattern, which upon RF excitation shows missing odd Shapiro steps, similar to the one reported in our previous work [Nat. Mater. 17, 875–880 (2018)]. Thickness dependent Ic field maps indicate the presence of topological edge states in thick Bi_1-xSb_x flakes, which hints towards a HOTI phase in this 3D DSM material. Whereas for thinner flakes, hybridization of the top and bottom edges could lead to trivial supercurrent characteristics. Our findings exhibit the non-trivial interplay between superconductivity and topology in an (expected) HOTI material, which holds great promise in quantum computing application as it can host Majorana zero-energy modes that are expected to demonstrate non-Abelian exchange statistics.