Doublon-holon binding, Mott transition, and fractionalized antiferromagnet in the Hubbard model

TL;DR

This paper introduces a new theoretical approach to the Hubbard model, emphasizing doublon-holon binding, to explain the Mott transition and fractionalized antiferromagnetic phases in bipartite lattices.

Contribution

It develops a saddle point solution incorporating doublon-holon binding within the Kotliar-Ruckenstein slave-boson framework, revealing a phase diagram with a continuous transition and a fractionalized Mott insulator.

Findings

Identifies a continuous transition from semimetal to antiferromagnetic insulator.

Discovers a Mott transition into an electron-fractionalized AF* phase.

Shows doublon-holon binding unifies key aspects of strong correlation phenomena.

Abstract

We argue that the binding between doubly occupied (doublon) and empty (holon) sites governs the incoherent excitations and plays a key role in the Mott transition in strongly correlated Mott-Hubbard systems. We construct a new saddle point solution with doublon-holon binding in the Kotliar-Ruckenstein slave-boson functional integral formulation of the Hubbard model. On the half-filled honeycomb lattice and square lattice, the ground state is found to exhibit a continuous transition from the paramagnetic semimetal/metal to an antiferromagnetic ordered Slater insulator with coherent quasiparticles at $U_{c1}$, followed by a Mott transition into an electron-fractionalized AF$^*$ phase without coherent excitations at $U_{c2}$. Such a phase structure appears generic of bipartite lattices without frustration. We show that doublon-holon binding unites the three important ideas of strong correlation: the coherent quasiparticles, the incoherent Hubbard bands, and the deconfined Mott insulator.