Anomalous de-phasing of quantum coherence phenomenon in superconductor/topological insulator (NbN/Bi1.95Sb0.05Se3) heterostructure

Abstract

The proximity-induced changes in magneto-transport properties of a topological insulator and a superconductor in an NbN/Bi1.95Sb0.05Se3 heterostructure are reported. Mechanically exfoliated single-crystal flake of Bi1.95Sb0.05Se3 topological insulator (TI) is partially covered with a ∼150 nm thick niobium nitride superconductor using DC magnetron sputtering. The temperature-dependent resistance, R(T) across the junction, shows double transitions at 11.5 K and 8 K, followed by the resistance upturn. MR on NbN covered region exhibit the typical BC2 behavior. At T < 20 K, the uncovered TI part exhibits weak anti-localization (WAL) for B < ± 1 T and a transition to negative MR at B > ± 3.5 T, while the junction shows only the WAL feature. As the temperature increases, the classical B2 dependence is retrieved on the TI and across the junction. The temperature coefficient of the phase coherence length obtained from the Hikami Larkin Nagaoka (HLN) analysis changes sign at the superconducting transition TC, evincing the de-phasing of the quantum coherence WAL phenomenon by the proximity of a superconductor. In contrast, the BC2 behavior of the superconductor is less affected by TI.