Finite momentum Cooper pairing in three-dimensional topological insulator Josephson junctions

Abstract

Unconventional superconductivity arising from the interplay between strong spin–orbit coupling and magnetism is an intensive area of research. One form of unconventional superconductivity arises when Cooper pairs subjected to a magnetic exchange coupling acquire a finite momentum. Here, we report on a signature of finite momentum Cooper pairing in the three-dimensional topological insulator Bi2Se3. We apply in-plane and out-of-plane magnetic fields to proximity-coupled Bi2Se3 and find that the in-plane field creates a spatially oscillating superconducting order parameter in the junction as evidenced by the emergence of an anomalous Fraunhofer pattern. We describe how the anomalous Fraunhofer patterns evolve for different device parameters, and we use this to understand the microscopic origin of the oscillating order parameter. The agreement between the experimental data and simulations shows that the finite momentum pairing originates from the coexistence of the Zeeman effect and Aharonov–Bohm flux.

Fermi-arc supercurrent oscillations in Dirac semimetal Josephson junctions

“…This work provides a flexible gate and magnetic field manipulations of Fermi-arc superconductivity. Compared with the finite momentum pairing observed in topological insulator 35 , we would like to clarify the differences between our work and that in Bi 2 Se 3 . First, Bi 2 Se 3 and Cd 3 As 2 belong to different topological phases, that is, Bi 2 Se 3 is a strong topological insulator protected by the time-reversal symmetry, while Cd 3 As 2 is a 3D Dirac semimetal with an extra C 4 rotational symmetry.…”

“…Critical current oscillations in superconductor-ferromagnet-superconductor junctions have provided evidences for both nonzero pairing momentum and 0-π transition [30][31][32] . More recently, quantum oscillations arising from in-plane Zeeman field induced finite momentum pairing have been demonstrated in Josephson systems of a Bi nanowire 33 , topological insulators [34][35][36] , and a Bi 0.97 Sb 0.03 topological semimetal 37,38 . In Dirac semimetal Cd 3 As 2 , each Dirac cone splits into two Weyl cones along the direction of the magnetic field 39 ( Supplementary Fig.…”

“…It has been reported that the in-plane orbital interference can also induce the critical current oscillations [34][35][36] . As illustrated in Fig.…”

“…As illustrated in Fig. 5a, we can model the phase difference ϕ 1 (x 1 ) − ϕ 2 (x 2 ) of the superconducting pairs, arising from the in-plane field orbital effect 35 :…”

“…For a surface pairing state, on the other hand, the trajectory will come along the circumferential direction of the flake. The surface related supercurrent can be expressed as 35 :…”