Thermodynamics vs. local density fluctuations in the metal/Mott-insulator crossover

TL;DR

This paper investigates the metal to Mott-insulator transition in fermionic atoms within an optical lattice, revealing how local and thermodynamic fluctuations behave differently across the crossover.

Contribution

It provides experimental insights into local density fluctuations and thermodynamics during the metal/Mott-insulator crossover using ultracold atoms.

Findings

Violation of local fluctuation-dissipation theorem in metallic phase

Convergence of local and thermodynamic fluctuations in Mott insulator

Absence of long-range density correlations in the insulator

Abstract

The crossover between a metal and a Mott insulator leads to a localization of fermions from delocalized Bloch states to localized states. We experimentally study this crossover using fermionic atoms in an optical lattice by measuring thermodynamic and local (on--site) density correlations. In the metallic phase at incommensurable filling we observe the violation of the local fluctuation--dissipation theorem indicating that the thermodynamics cannot be explained by local observables. In contrast, in the Mott-insulator we observe the convergence of local and thermodynamic fluctuations indicating the absence of long--range density-density correlations.