SU(2) gauge theory of the Hubbard model: Emergence of an anomalous metallic phase near the Mott critical point

TL;DR

This paper introduces an SU(2) gauge theory for the Hubbard model, explaining the emergence of an anomalous metallic phase with no electron quasiparticles near the Mott transition, via local pairing fluctuations.

Contribution

It develops an SU(2) gauge theory framework extending previous U(1) models to account for local density and pairing fluctuations, revealing a new intermediate metallic phase.

Findings

Identification of an intermediate phase with soft density modes and gapped pairing modes

Demonstration of a metallic phase lacking electron quasiparticles

Extension of gauge theory approach to include local pairing fluctuations

Abstract

We propose one possible mechanism for an anomalous metallic phase appearing frequently in two spatial dimensions, that is, local pairing fluctuations. Introducing a pair-rotor representation to decompose bare electrons into collective pairing excitations and renormalized electrons, we derive an SU(2) gauge theory of the Hubbard model as an extended version of its U(1) gauge theory\cite{Florens,LeeLee} to allow only local density fluctuations. Since our effective SU(2) gauge theory admits two kinds of collective bosons corresponding to pair excitations and density fluctuations respectively, an intermediate phase appears naturally between the spin liquid Mott insulator and Fermi liquid metal of the U(1) gauge theory,\cite{Florens,LeeLee} characterized by softening of density-fluctuation modes as the Fermi liquid, but gapping of pair-excitation modes. We show that this intermediate phase is identified with an anomalous metallic phase because there are no electron-like quasiparticles although it is metallic.