Barriers to Macroscopic Superfluidity and Insulation in a 2D Aubry-Andr\'e Model

Abstract

We study the ground state phases of interacting bosons in the presence of a 2D Aubry-Andr\'e potential. By using a a mean-field percolation analysis, we focus on several superlattice and quasicrystalline regimes of the 2D Aubry-Andr\'e model, including generalisations that account for a tilting or skewing of the potential. We show that barriers to the onset of macroscopic phases naturally arise from weakly modulated domains in the 2D Aubry-Andr\'e model. This leads to the formation of mixed phases, in which the macroscopic properties are dominated by a minority of the system. The phase diagrams then exhibit substantially different features when compared against crystalline systems, including a lobe-like or wave-like appearance of the Bose glass, sharp extrusions and extended domains with weak percolation. By studying the 2D Aubry-Andr\'e model across multiple regimes, we have shown that the unique properties of mixed phases are not distinct to a small set of parameters.