Unconventional Josephson Effect in a topological Kondo insulator

Proximity-induced superconductivity in three dimensional (3D) topological insulators forms a new quantum phase of matter and harbors exotic quasiparticles such as Majorana bound states. One of the biggest drawbacks of the commonly studied 3D topological insulators is having conducting bulk that obscures the role of surface states. Introducing superconductivity in topological Kondo insulators such as SmB₆ is particularly promising due to their robust insulating bulk at low temperatures. In this work, we develop an unconventional Josephson junction by coupling superconducting Nb leads to the surface states of a SmB₆ crystal. We observe a distinct critical current at low temperatures that exhibits a Fraunhofer diffraction pattern with the application of an out-of-plane magnetic field. The appearance of Shaphiro steps under microwave irradiation gives further evidence of a Josephson Effect. The Fraunhofer patterns show an anomalous hysteresis with magnetic field sweep direction suggesting coexistence of ferromagnetism with superconductivity in the topological surface states of SmB₆. The experimental work will advance the current understanding of topologically nontrivial superconductors and emergent states associated with such unconventional superconducting phases.