Coupled two-component atomic gas in an optical lattice

TL;DR

This paper investigates the ground state properties of a coupled two-component ultracold atomic gas in a 1D optical lattice, revealing a temperature-driven phase transition with topological features for fermions due to internal and kinetic energy interplay.

Contribution

It provides an ab initio analysis of how internal atomic structure influences band topology and phase transitions in optical lattices, extending to higher dimensions.

Findings

Presence of multiple local minima in energy bands due to internal structure.

Observation of a temperature-induced phase transition across a resonance.

Topological change in Fermi surface for fermionic systems.

Abstract

We present an ab initio study of the ground state of an ideal coupled two-component gas of ultracold atoms in a one dimensional optical lattice, either bosons or fermions. Due to the internal two-level structure of the atoms, the Brillouin zone is twice as large as imposed by the periodicity of the lattice potential. This is reflected in the Bloch dispersion curves, where the energy bands regularly possess several local minima. As a consequence, when the system parameters are tuned across a resonance condition, a non-zero temperature phase transition occurs which arises from an interplay between internal and kinetic atomic energies. For fermions, this phase transition is of topological character since the structure of the Fermi surface is changed across the critical value. It is shown that these phenomena are also expected to occur for two and three dimensional optical lattices.