Observation of long-range co-tunnling from Chiral Hinge Modes in the Magnetic Topological Superconductor Fe(Te, Se)

A key challenge in topological systems is finding unique signatures of their boundary modes. This is especially true in topological superconductors where the bulk is gapped, but the superfluid can short-circuit transport signatures seen in quantum Hall states. A particularly promising candidate is Fe(Te,Se), which is predicted to host a 1D high-order topological superconducting (1D-HOTSC) state. This can emerge either from the bulk sign-changing order parameter or from the combination of intrinsic magnetism and topological superconductivity. Here, we present systematic tunneling experiments to test the existence of 1D-HOTSC mode. Initially, we observe an anomalous conductance plateau signal centered around zero bias when electrons tunnel along the hinges of our Fe(Te,Se) device in the topologically nontrivial phase. Remarkably, this anomalous conductance plateau disappears when the current source and ground are no longer connected by the same hinge, suggesting the nonlocal co-tunneling processes originating from a propagating TSC hinge mode. To confirm this originates from nontrivial topology, we have tested devices with different Te/Se composition that possess similar superconducting transition temperatures without the bulk topological band inversion. As expected, such conductance signal disappears in these samples. Additionally, the conductance plateau is robust to applied magnetic field and temperature, so long as the long-range magnetic order detected by Kerr rotation is maintained. Thus, our results are consistent with chiral TSC modes rather than trivial superconducting states.