Exact numerical diagonalization of one-dimensional interacting electrons nonadiabatically coupled to phonons

TL;DR

This paper uses exact numerical diagonalization to investigate how non-adiabatic electron-phonon interactions influence phase transitions and lattice properties in one-dimensional charge transfer crystals, revealing significant effects on transition nature and phonon quantum uncertainty.

Contribution

It provides a detailed analysis of non-adiabatic effects on phase transitions in 1D electron-phonon systems using exact diagonalization, highlighting limitations of adiabatic approximations.

Findings

Non-adiabaticity smooths electronic property variations.

Lattice properties exhibit squeezing and antisqueezing.

Quantum phonon uncertainty is a key measure of nonadiabaticity.

Abstract

We study the role of non-adiabatic Holstein electron-phonon coupling on the neutral-ionic phase transition of charge transfer crystals which can be tuned from continuous to discontinuous, using exact numerical diagonalization. The variation of electronic properties through the transition is smoothed by nonadiabaticity. Lattice properties are strongly affected, and we observe both squeezing and antisqueezing, depending on details of the adiabatic potentials, and identify the quantum uncertainty of the phonons as the most sensitive measure of nonadiabaticity. The adiabatic limit is regular for a continuous transition but turns out completely inadequate near a discontinuous transition. The relevance of coherent state approaches is assessed critically.