Aharonov-Casher effect with vortices in an amorphous superconductor

A trajectory of a magnetic moment in an electric field results in the acquisition of a topological phase called the Aharonov-Casher (A-C) phase, analogous to the A-B phase acquired by a charged particle in a magnetic field. In condensed matter, experiments demonstrating the A-C effect are relatively few, the earliest being for superconducting vortices traversing a fabricated Josephson-junction array. In that regular geometry, a periodic response to induced charge was observed. In an irregular geometry, in analogy with universal conductance fluctuations, a complex quasi-periodic respinse may be expected.
An amorphous superconductor close to a superconductor-insulator transition (SIT) provides such a complex multiply connected region for superconducting vortices to interfere, as indicated by recent studies. In this study with amorphous indium oxide close to a disorder driven SIT, we introduce vortices in the system by applying a perpendicular magnetic field. The motion of these vortices around superconducting islands generates a complex interference pattern in the form of a spontaneous voltage that is tunable with both gate voltage and magnetic field. This effect is a demonstration of the quantum behavior of Josephson vortices which are present in the system close to the SIT.