A study of single Josephson junctions using proximity induced topological superconductivity in bulk insulating Bi_0.8Sb_1.2Te₃

A hybrid system of an s-wave superconductor with a 2D topological insulator behaves like a spinless p-wave superconductor and can be used to develop Majorana based qubits. Bismuth antimony telluride(Bi_xSb_2-xTe₃ or BST) is a 2D topological insulator whose composition can be tuned during the growth process to have the Fermi level only cross surface states. This suppression of bulk carriers is needed to realize a purely topological superconductivity. From ARPES data of various compositions, Bi_0.8Sb_1.2Te₃ is found to be insulating in the bulk and hence the carriers are topological surface states. Molecular beam epitaxy is used to grow thin films of Bi_0.8Sb_1.2Te₃, which are used as the weak link in fabricating single Josephson junctions of varying lengths with niobium electrodes. Junctions of lengths varying from 40 to 80 nm were studied. Differential conductance measurements and magnetic diffraction patterns are used to characterize the junctions.