Quantum Oscillations in Topological Insulator Bi2Te2Se Microwires Contacted with Superconducting In2Bi Leads

We studied the magnetoresistance (MR) of polycrystal Bi2Te2Se topological insulator (TI) microwires contacted with superconducting In2Bi leads. Bi2Te2Se has a simple band structure with a single Dirac cone on the surface and a large non-trivial bulk gap of 300 meV. To study the TI/SC interface, the Bi2Te2Se glass-coated microwire with a diameter of d = 17 µm was connected to copper leads on one side using superconducting alloy In2Bi (Tc = 5.6 K), and on the other side using gallium. The topologically nontrivial 3D superconductor (SC) In2Bi has proximity-induced superconductivity of topological surface states. To eliminate conventional contribution to superconductivity from the bulk, the resulting edge states of the TI/SC contact area were studied in magnetic fields above Hc2 in In2Bi. The h/2e oscillations of magnetoresistance (MR) in longitudinal and transverse magnetic fields (up to 1 T) at the TI/SC interface were observed at various temperatures (4.2 k–1.5 K). To explain the observed oscillations, we used magnetic flux quantization, which requires a multiply connected geometry where flux can penetrate into normal regions surrounded by a superconductor. The effective width of the closed superconducting area of the TI/SC interface is determined to be 15 nm from an analysis of FFT spectra and the beats of the MR oscillations for two different directions of magnetic field.