Instability of insulating states in optical lattices due to collective phonon excitations

TL;DR

This paper investigates how collective phonon excitations, arising from intersite atomic interactions, can destabilize insulating states in optical lattices, potentially leading to delocalization of atoms.

Contribution

It introduces the concept that self-organized collective phonons can significantly influence atomic localization, challenging the stability of insulating states in optical lattices.

Findings

Collective phonons can cause insulating states to become delocalized.

Both long-range and local interactions are affected by these phonon excitations.

The Lindemann criterion is used to determine stability regions.

Abstract

The role of collective phonon excitations on the properties of cold atoms in optical lattices is investigated. These phonon excitations are collective excitations, whose appearance is caused by intersite atomic interactions correlating the atoms, and they do not arise without such interactions. These collective excitations should not be confused with lattice vibrations produced by an external force. No such a force is assumed. But the considered phonons are purely self-organized collective excitations, characterizing atomic oscillations around lattice sites, due to intersite atomic interactions. It is shown that these excitations can essentially influence the possibility of atoms to be localized. The states that would be insulating in the absence of phonon excitations can become delocalized when these excitations are taken into account. This concerns long-range as well as local atomic interactions. To characterize the region of stability, the Lindemann criterion is used.