Mechanism for Synchronization of Charge Oscillations in Dimer Lattices

TL;DR

This paper explores the mechanism behind synchronized charge oscillations in dimerized systems, highlighting the role of pseudospin dynamics and the impact of electron interactions on synchronization.

Contribution

It introduces a pseudospin-based model explaining charge oscillation synchronization and examines how electron interactions influence this process.

Findings

Pseudospin tilt facilitates synchronization across wave numbers.

Synchronization occurs regardless of initial conditions.

Excitons can hinder charge oscillation synchronization.

Abstract

We discuss the mechanism and the conditions for the appearance of synchronized charge oscillations which have been observed experimentally and theoretically after strong photoexcitation of dimerized systems. In the Hubbard model with on-site repulsion, the Bloch equations for a wave-number-dependent pseudospin -- whose components describe the charge-density difference, current density, and bond density between the two sublattices -- involve an alternatingly tilted pseudomagnetic field, which assists the synchronization of pseudospins with different wave numbers, irrespective of the initial condition. This fact is numerically confirmed by the dynamics in finite lattices based on the exact diagonalization method. In the presence of nearest-neighbor repulsion, however, the synchronization can be hindered by excitons. Therefore, the excitation of a sufficiently large density of free electron-hole pairs, but low density of excitons, is needed to achieve synchronization.