Josephson Junctions with epitaxial topological insulator SmB₆ thin films

Since Josephson junctions with an s-wave superconductor (SC) and a topological insulator (TI) has been predicted to be a possible venue for hosting elusive Majorana Fermions, many experimental efforts have been made with HgTe and Bi-based TIs. Recently, TI SmB₆ has gained attention as a promising material for such applications because its true bulk insulating state can eliminate undesirable bulk contribution to the Josephson effect. We have previously demonstrated the superconducting proximity effect in in-situ deposited SC-TI Nb/SmB₆ heterostructures as a result of Nb superconductivity induced in the surface state of SmB₆. In this work, we show transport characteristics of Nb-SmB₆-Nb Josephson junctions, including DC I-V characteristics, their magnetic field dependence, and the AC Josephson effect. Epitaxial SmB₆ thin films are grown by a co-sputtering process. To secure high interfacial quality between Nb and SmB₆, Nb layers are deposited on the SmB₆ layers in-situ, and a top-down process including e-beam lithography and ion milling was utilized to define Josephson junction structures with a gap width of 50 nm and the lateral dimension of 1 µm. We discuss the observed Josephson effect in terms of the high-transparency interface and the true insulating bulk nature of SmB₆.