by Dr. Biplab Bhattachayya, University of Twente, Netherlands

Abstract:

Edge transport in quantum materials, when arising from symmetry-protected  topological channels, provides robust and dissipationless conduction that directly reflects the nontrivial topology of the bulk. Building on this concept, higher-order topological edge states in 3D materials, protected by crystalline symmetries, form hinge-localized 1D channels, where induced superconductivity can enable potential applications in topological quantum computing. We have performed a comprehensive study of Josephson supercurrent in Nb-BiSb(3%)-Nb junctions fabricated on flakes of varying thicknesses, widths and junction lengths. The critical supercurrent modulates with a magnetic field in a SQUID-like pattern, which upon radio-frequency excitation shows missing odd Shapiro steps. Interestingly, we found a strong correlation between fractional Shapiro steps, indicative of a 4π-periodic supercurrent, and the presence of long-ballistic hinge-localized modes. Tight-binding calculations further support our experimental finding of multiple hinge channels, arising from structural irregularities, that contribute to the total edge supercurrent. Additionally, an anomalous current-phase-relation in asymmetric SQUID devices reveal the coexistence of 1D Rashba and higher-order topological states.