posted on 2024-02-07, 19:06authored byDong-Xia Qu, Joseph J. Cuozzo, Nick E. Teslich, Keith G. Ray, Zurong Dai, Tian T. Li, George F. Chapline, Jonathan L. DuBois, Enrico Rossi
Superconducting topological systems
formed by a strong 3D topological
insulator (TI) in proximity to a conventional s-wave
superconductor (SC) have been intensely studied, as they may host
Majorana zero modes. However, there are limited experimental realizations
of TI-SC systems in which robust superconducting pairing is induced
on the surface states of the TI and a topological superconducting
state is established. Here, we fabricate a TI-SC system by depositing,
via a focused ion beam, tungsten (W) nanoscale clusters on the surface
of TI Bi0.91Sb0.09. We find that the resulting
heterostructure supports phase-slip lines (PSLs) that act as effective
Josephson junctions (JJs). We probe the response of the system to
microwave radiation. We find that for some ac frequencies, and powers,
the resulting Shapiro steps’ structure of the voltage–current
characteristic exhibits a missing first step and an unexpectedly wide
second Shapiro step. The theoretical analysis of the measurements
shows that the unusual Shapiro response arises from the interplay
between a static JJ and a dynamic one and allows us to identify the
conditions under which the missing first step can be attributed to
the topological nature of the JJs formed by the PSLs. Our results
suggest an approach to induce superconductivity in a TI, a route to
realizing highly transparent topological JJs, and show how the response
of superconducting systems to microwave radiation can be used to infer
the dynamics of PSLs. Highly transparent topological junctions are
promising candidates to realize vector field sensors with very high
sensitivity. In addition, due to the nontrivial Berry phase of the
TI’s surface states such junctions can be in a topological
state which is ideal to create topologically protected qubits.