Superconducting Proximity Effect in Magnetically-Doped Topological Insulators using Bulk Single Crystals*

Superconducting proximity effect on magnetic topological insulators (TIs) is expected to induce unconventional superconductivity, some of which can host the Majorana fermion. Recently, we observed some unusual behaviors on Nb/Fe-doped TI/ Nb Josephson junctions: e.g., a unique three-peak structure and a 4π-periodic Josephson current. However, those origins are still under debate due to possible contributions from the bulk and the edge modes to the proximity effect.
In this study, we prepared another magnetic TI with a high bulk resistivity and fabricated its Josephson junctions without edge contacts. As a result, a similar three-peak structure was also observed, suggesting that the observed unique behaviors found in the former junction also came from the surface contribution. Furthermore, we observed a unique magnetic response possibly related to bulk magnetic properties. We believe that those results promote our understanding of the proximity effect on topological materials.