Description
Epitaxial semiconductor-superconductor hybrid materials provide a novel highly-tunable platform to study emergent quantum phenomena, taking advantage of gate-controlled density, ballistic transport, and non-sinusoidal current-phase relations. Recently, hybrid Josephson junction arrays have been used to probe the gate-controlled superconductor-insulator transition (SIT), where Josephson couplings can be tuned to be greater than or less than the charging energy of the islands. A perpendicular magnetic field introduces frustration, leading to complex ground states that depend on the geometry of the array. The talk will focus on two-dimensional Josephson junction arrays in the dice lattice geometry, that are predicted to host flat bands when frustrated. I will discuss our efforts to map out the phase diagram as a function of frustration: Frustrations commensurate with the lattice geometry lead to the formation of vortex lattices, which are absent at incommensurate values of frustration. When the array is frustrated by half a flux quantum per plaquette, quantum interference localizes individual Cooper pairs, corresponding to the formation of a flat-band system.
