Interface effect in Nb-Bi2Te3 hybrid structure

An array of Nb strips was fabricated on a Bi2Te3 thin film. Transport measurements show that an upturn of the resistance occurs below the Nb superconducting transition temperature. Corresponding to this resistance upturn, a differential resistance peak around zero bias and a prominent negative magnetoresistance at low magnetic fields are observed. The resistance upturn, differential resistance peak, and negative magnetoresistance can be suppressed by increasing measurement current, temperature, and applied magnetic field. We explain these phenomena in terms of an energy barrier effect induced by the Nb superconducting gap and the suppression of Andreev reflection due to the low transparency at the Nb-Bi2Te3 interface.