Fluctuation-Driven Quantum Phase Transitions in Clean Itinerant Ferromagnets

TL;DR

This paper investigates how soft particle-hole modes influence quantum phase transitions in clean itinerant ferromagnets, revealing fluctuation-induced first or second order transitions and aligning with recent experimental findings.

Contribution

It introduces a renormalized mean-field theory accounting for fluctuations, showing the transition order depends on microscopic parameters and analyzing stability via renormalization group methods.

Findings

Soft modes invalidate Hertz's mean-field theory for d ≤ 3.

Fluctuation effects can induce first or second order transitions.

Results agree with recent experimental observations.

Abstract

The quantum phase transition in clean itinerant ferromagnets is analyzed. It is shown that soft particle-hole modes invalidate Hertz's mean-field theory for $d \leq 3$. A renormalized mean-field theory predicts a fluctuation-induced first order transition for $1 < d \leq 3$, whose stability is analyzed by renormalization group techniques. Depending on microscopic parameter values, the first order transition can be stable, or be pre-empted by a fluctuation-induced second order transition. The critical behavior at the latter is determined. The results are in agreement with recent experiments.