Doublon-holon binding as origin of Mott transition and fractionalized spin liquid -- Asymptotic solution of the Hubbard model in the limit of large coordination

TL;DR

This paper presents an analytical solution to the Hubbard model on the Bethe lattice at large coordination, revealing that doublon-holon binding drives the Mott transition and stabilizes a fractionalized spin liquid insulator.

Contribution

It introduces a doublon-holon binding theory that differs from dynamical mean-field theory, capturing intersite spinon correlations and the emergence of a deconfined spin liquid phase.

Findings

Doublon-holon binding causes a continuous Mott transition.

The spin liquid insulator is stabilized by a deconfined U(1) gauge field.

The theory predicts a fractionalized gapless spin liquid phase.

Abstract

An analytical solution of the Mott transition is obtained for the Hubbard model on the Bethe lattice in the large coordination number ($z$) limit. The excitonic binding of doublons (doubly occupied sites) and holons (empty sites) is shown to be the origin of a continuous Mott transition between a metal and an emergent quantum spin liquid insulator. The doublon-holon binding theory enables a different large-$z$ limit and a different phase structure than the dynamical meanfield theory by allowing intersite spinon correlations to lift the $2^N$-fold degeneracy of the local moments in the insulating phase. We show that the spinons are coupled to doublons/holons by a dissipative compact U(1) gauge field that is in the deconfined phase, stabilizing the spin-charge separated gapless spin liquid Mott insulator.