Flux-parity controlled superconducting diode effect in topological insulator Josephson junctions

The superconducting diode effect (SDE), in which supercurrent is asymmetric in applied current bias, can be observed when time reversal and inversion symmetries are broken in a Josephson junction. Recently, changes in the sign of the SDE have been correlated with possible topological phase transitions in certain regimes of linear Josephson junctions. Here we report a flux-parity controlled SDE in Corbino-geometry Josephson junctions, where even/odd flux parity states show a SDE alternating in sign. These junctions are fabricated on a single surface of a bulk-insulating three-dimensional topological insulator and can be used for probing signatures of Majorana states that are theoretically present within the junctions under a magnetic field. We fabricate high-quality niobium Josephson junctions on tellurium-capped Sn-doped Bi_1.1Sb_0.9Te₂S (Sn-BSTS) single crystals, with junctions showing high transparency. Additionally, different Corbino-style geometries enable Josephson interferometry within a single junction, allowing us to explore the skewed current-phase relation. Our analysis attributes the flux-parity controlled SDE to a topological phase, with opposite diode polarity directly reflecting the sign change of the periodic boundary conditions for an even/odd number of Josephson vortices in the junction.