  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 3D 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.
