Doublon dynamics in the extended Fermi Hubbard model

TL;DR

This paper investigates the dynamics and stability of doublons in the extended Fermi Hubbard model using exact diagonalization, revealing how doublon decay and stability depend on interaction strength and fermion presence.

Contribution

It provides a detailed analysis of doublon dynamics, decay timescales, and the influence of additional fermions, offering new insights into doublon stability in strongly correlated systems.

Findings

Short-time decay scale ~1/U

Long-time decay fraction scales as 1/U^2

Presence of additional fermions enhances doublon stability

Abstract

Two fermions occupying the same site of a lattice model with strongly repulsive Hubbard-type interaction U form a doublon, a long-living excitation the decay of which is suppressed because of energy conservation. By means of an exact-diagonalization approach based on the Krylov-space technique, we study the dynamics of a single doublon, of two doublons, and of a doublon in the presence of two additional fermions prepared locally in the initial state of the extended Hubbard model. The time dependence of the expectation value of the double occupancy at the different sites of a large one-dimensional lattice is analyzed by perturbative arguments. In this way the spatiotemporal evolution of the doublon can be understood. The initial decay takes place on a short time scale 1/U, and the long-time average of the decayed fraction of the total double occupancy scales as 1/U^2 . We demonstrate how the dynamics of a doublon in the initial state is related to the spectrum of two-fermion excitations obtained from linear-response theory, we work out the difference between doublons composed of fermions vs doublons composed of bosons, and we show that despite the increase of phase space for inelastic decay processes, the stability of a doublon is enhanced by the presence of additional fermions on an intermediate time scale.