Fluctuation-driven quantum phase transitions in clean itinerant ferromagnets

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< or =3. A renormalized mean-field theory predicts a fluctuation-induced first order transition for 1<d< or =3, whose stability is analyzed by renormalization group techniques. Depending on microscopic parameter values, the first order transition can be stable, or be preempted by a fluctuation-induced second order transition. The critical behavior at the latter is determined. The results are in agreement with recent experiments.