Critical field theory for ferromagnetic quantum criticality in the strong coupling regime of Hertz-Moriya-Millis theory

TL;DR

This paper introduces a U(1) slave spin-rotor theory to extend Hertz-Moriya-Millis theory, describing a transition from Fermi-liquid to bad metal with emergent localized moments at ferromagnetic quantum critical points.

Contribution

It develops a novel slave spin-rotor framework to generalize quantum criticality theories for ferromagnetic transitions in strongly correlated metals.

Findings

Identifies a metal-metal transition to a bad metal phase.

Proposes emergence of localized magnetic moments at quantum criticality.

Generalizes Hertz-Moriya-Millis theory for strong coupling regimes.

Abstract

We develop U(1) slave spin-rotor theory, suggesting a metal-metal transition from Landau's Fermi-liquid state to a bad metal phase, as U(1) slave charge-rotor theory [Phys. Rev. B {\bf 70}, 035114 (2004)] describes a metal-insulator transition from Landau's Fermi-liquid state to a spin-liquid phase. U(1) slave spin-rotor formulation allows us to generalize Hertz-Moriya-Millis theory for ferromagnetic quantum phase transitions, replacing Landau's Fermi-liquid state with an incoherent metallic phase. As a result, we argue that localized magnetic moments emerge to govern quantum critical physics in bad metals.