Doping induced superconductivity in topological insulator SnBi₂Te₄

Topological superconductors (TSCs) can host Majorana bound states and are promising platforms for quantum computation. TSCs can be realized by constructing artificial heterostructures with a topological insulator in proximity to an s-wave superconductor. Another approach is through the synthesis or discovery of materials with both nontrivial topological electronic structures and superconducting properties. A recent report showed that the topological insulator SnBi₂Te₄ becomes a bulk superconductor when substituting Sn with In [1]. The superconducting critical temperature of the indium doped compound was raised to 1.85K as the indium ratio x is increased to 0.61 in Sn_1-xIn_xBi₂Te₄. Here we use scanning tunneling microscope (STM) to investigate in situ cleaved Sn_0.4In_0.6Bi₂Te₄ at 40mK. The Te-terminated surface shows a single U-shaped superconducting gap with size of 0.3meV, as well as Dirac bands outside the gap. The evolution of a vortex lattice with the magnetic field and spatial distribution of zero-bias conductance near a vortex core indicate a weak-coupling s-wave BCS superconductor, with coherence length of 17nm. Adjusting doping is required so that the Dirac point is located near the Fermi level and the topological surface states are properly gapped by the induced bulk superconductivity.

[1] M. A. McGuire et al, Phys. Rev. Materials 7, 034802 (2023)