Charge and spin density wave ordering transitions in strongly correlated metals

TL;DR

This paper investigates the quantum phase transition from a heavy fermionic metal to a charge or spin density wave ordered state, revealing a crossover in critical behavior and characteristics of the quasiparticle spectrum.

Contribution

It introduces a large-dimensionality model coupling Ising spins and fermions, analyzing critical exponents and crossover phenomena near density wave transitions in strongly correlated metals.

Findings

Critical exponent $z u = 1$ at low energies

Crossover to $z u = 1/2$ criticality above energy scale $\Gamma$

Presence of a narrow quasiparticle band and Hubbard bands in the spectrum

Abstract

We study the quantum transition from a strongly correlated metal, with heavy fermionic quasiparticles, to a metal with commensurate charge or spin density wave order. To this end, we introduce and numerically analyze a large dimensionality model of Ising spins in a transverse field, coupled to two species of fermions; the analysis borrows heavily from recent progress in the solution of the Hubbard model in large dimensions. At low energies, the Ising order parameter fluctuations are characterized by the critical exponent $z \nu = 1$, while above an energy scale, $\Gamma$, there is a crossover to $z\nu = 1/2$ criticality. We show that $\Gamma$ is of the order of the width of the heavy quasiparticle band, and can be made arbitrarily small for a correlated metal close to a Mott-Hubbard insulator. Therefore, such a correlated metal has a significant intermediate energy range of $z\nu=1/2$ behavior, a single particle spectrum with a narrow quasiparticle band, and well-formed analogs of the lower and upper Hubbard bands; we suggest that these features are intimately related in general.