Coexistence of superfluid and Mott phases of lattice bosons

TL;DR

This paper investigates the coexistence of superfluid and Mott-insulating phases in optical lattices, analyzing their spatial separation, collective modes, and phase transitions in inhomogeneous bosonic systems.

Contribution

It provides a theoretical framework for understanding the coexistence and properties of superfluid and Mott phases in inhomogeneous lattice boson systems.

Findings

Superfluid forms a trapped layer between Mott-insulating regions.

Derived the collective mode structure of the superfluid.

Estimated critical temperatures for superfluid-normal phase transition.

Abstract

Recent experiments on strongly-interacting bosons in optical lattices have revealed the co-existence of spatially-separated Mott-insulating and number-fluctuating phases. The description of this inhomogeneous situation is the topic of this Letter. We establish that the number-fluctuating phase forms a superfluid trapped between the Mott-insulating regions and derive the associated collective mode structure. We discuss the interlayer's crossover between two- and three-dimensional behavior as a function of the lattice parameters and estimate the critical temperatures for the transition of the superfluid phase to a normal phase.