Holon-Doublon Binding as the Mechanism for the Mott transition

TL;DR

This paper investigates the holon-doublon binding mechanism as the cause of the Mott transition in Hubbard models, revealing a discontinuous transition influenced by spin polarization and lattice structure.

Contribution

It introduces a comprehensive study of holon-doublon binding as the Mott transition mechanism, extending analysis to non-polarized systems with finite HD density using novel approaches.

Findings

Holon-doublon binding explains the Mott transition.

Discontinuous transition occurs in non-polarized systems.

Results align with numerical data on triangular lattices.

Abstract

We study the binding of a holon to a doublon in a half-filled Hubbard model as the mechanism of the zero-temperature metal-insulator transition. In a spin polarized system and a non-bipartite lattice a single holon-doublon (HD) pair exhibits a binding transition (e.g., on a face-centred cubic lattice), or a sharp crossover (e.g., on a triangular lattice) corresponding well to the standard Mott transition in unpolarized systems. We extend the HD-pair study towards non-polarized systems by considering more general spin background and by treating the finite HD density within a BCS-type approximation. Both approaches lead to a discontinuous transition away from the fully polarized system and give density correlations consistent with numerical results on a triangular lattice.