Observation of unconventional proximity induced superconducting effects in Bi2Se3 flakes

Abstract

Topological superconductors (TSCs) are the materials with superconducting gap in bulk and exotic quasiparticles form gapless edge state. These quasiparticles can be employed as topological quantum bits for execution of quantum computation. Intrinsic TSCs are very rare in nature but artificial TSCs can be engineered by combining topological insulators with s-wave conventional superconductors. Hence recently hybrid structure composed of topological insulator and superconductor has been subject of research in condensed matter physics. In this paper, we use Bi2Se3 topological insulator thin flakes and tungsten (W) superconducting electrodes are deposited by using FIB based gas injection system (GIS). Fabricated Bi2Se3 flake/W hybrid structures were used to investigate induced superconductivity in Bi2Se3 flake via electric transport measurements. The resistance of the flake shows a drastic and significant decrease (8.4%) when the electrodes become superconducting. The superconducting transition (8.4%) is observed even though the length of Bi2Se3 flake between the superconducting contacts was 1.38 μm (≫ superconducting coherence length). Surprisingly, we find that resistance of Bi2Se3 flake shows an abrupt increase just before the transition temperature of superconducting electrodes (T < Tc) due to presence of electron-electron interaction. We also observe that the magnetoresistance of the flake is negative below transition temperature (T < Tc), but above transition temperature (T > Tc) magnetoresistance becomes positive due to the effects of superconducting electrodes which we discussed here in detail and it may help in constructing the topological superconductor.