Quasiparticle undressing in a dynamic Hubbard model: exact diagonalization study

TL;DR

This study uses exact diagonalization to show that pairing in a dynamic Hubbard model leads to quasiparticle 'undressing', decreasing effective mass and increasing spectral weight, similar to phenomena observed in high-Tc cuprates.

Contribution

It demonstrates that pairing in a dynamic Hubbard model causes quasiparticle 'undressing', contrasting with traditional models where pairing causes 'dressing'.

Findings

Pairing lowers effective mass and increases quasiparticle weight.

Spectral weight shifts from high to low frequencies upon pairing.

Behavior resembles experimental observations in high-Tc cuprates.

Abstract

Dynamic Hubbard models have been proposed as extensions of the conventional Hubbard model to describe the orbital relaxation that occurs upon double occupancy of an atomic orbital. These models give rise to pairing of holes and superconductivity in certain parameter ranges. Here we explore the changes in carrier effective mass and quasiparticle weight and in one- and two-particle spectral functions that occur in a dynamic Hubbard model upon pairing, by exact diagonalization of small systems. It is found that pairing is associated with lowering of effective mass and increase of quasiparticle weight, manifested in transfer of spectral weight from high to low frequencies in one- and two-particle spectral functions. This 'undressing' phenomenology resembles observations in transport, photoemission and optical experiments in high T_c cuprates. This behavior is contrasted with that of a conventional electron-hole symmetric Holstein-like model with attractive on-site interaction, where pairing is associated with 'dressing' instead of 'undressing'.