Quantum Critical Behavior in Disordered Itinerant Ferromagnets: Instability of the Ferromagnetic Phase

TL;DR

This paper develops an effective field theory to describe quantum critical behavior in disordered itinerant ferromagnets, revealing that Goldstone modes do not influence critical exponents and confirming the phase transition's nature from the ferromagnetic side.

Contribution

It introduces a new effective field theory for the ferromagnetic phase near quantum criticality, complementing previous studies on the paramagnetic side, and clarifies the role of Goldstone modes.

Findings

Goldstone modes do not affect critical behavior

Critical exponents match those from the paramagnetic phase

The theory describes the transition approaching from the ferromagnetic side

Abstract

An effective field theory is derived that describes the quantum critical behavior of itinerant ferromagnets as the transition is approached from the ferromagnetic phase. This complements a recent study of the critical behavior on the paramagnetic side of the phase transition, and investigates the role of the ferromagnetic Goldstone modes near criticality. We find that the Goldstone modes have no direct impact on the critical behavior, and that the critical exponents are the same as determined by combining results from the paramagnetic phase with scaling arguments.