Multifractals competing with solitons on Fibonacci optical lattices

Abstract

We study stationary states for the nonlinear Schrödinger equation on Fibonacci lattices, which are expected to be realized by Bose–Einstein condensates loaded into an optical lattice. When the model does not have a nonlinear term, the wavefunctions and the spectrum are known to show fractal structures. Such wavefunctions are termed critical. We present a phase diagram of the energy spectrum for varying the nonlinearity. It consists of three portions: a forbidden region, the spectrum of critical states and the spectrum of stationary solitons. We show that the energy spectrum of critical states remains intact, irrespective of the nonlinearity in the large number of stationary solitons.