Probing Majorana physics in topological insulator-based Josephson junctions through current-phase relation measurements

The interplay between superconductivity and topology creates ideal conditions for engineering Majorana bound states (MBSs), non-Abelian quasiparticles with potential applications in fault-tolerant quantum computing. Current-phase relation (CPR) measurements in Josephson junctions (JJs) with topological insulators (TIs) as weak links serve as a powerful technique to identify signatures of MBSs and differentiate them from trivial effects. Here, using an asymmetric SQUID technique, we probe the CPR in planar van der Waals (vdW) JJs combining the superconducting NbSe₂ and two different few-layer-thick TIs: Bi₂Se₃ and Sn-doped BiSbTe₂S (Sn-BSTS). When one flux quantum threads the junction, we observe an anomalous peak–dip structure in the CPR that initially appears consistent with that expected from hybridized MBSs at the junction edge. Our detailed analysis, however, reveals that in Bi₂Se₃-based JJs this anomaly originates from a non-uniform supercurrent distribution that produces a non-reciprocal CPR with complex magnetic-field dependence, indicating the absence of MBS signatures. However, in Sn-BSTS devices, we observe additional unconventional features whose origin remains unclear and may point toward more exotic physics possibly related to MBS formation.