Influence of rare regions on magnetic quantum phase transitions

TL;DR

This paper investigates how rare regions caused by quenched disorder influence the critical behavior of itinerant quantum magnets, revealing their differing effects on antiferromagnetic and ferromagnetic transitions.

Contribution

It demonstrates that rare regions destroy the critical fixed point in antiferromagnets but do not affect ferromagnets due to long-range interactions.

Findings

Rare regions destroy the critical fixed point in antiferromagnets.

In itinerant ferromagnets, critical behavior remains unaffected by rare regions.

The study clarifies the role of quenched disorder in quantum phase transitions.

Abstract

The effects of quenched disorder on the critical properties of itinerant quantum magnets are considered. Particular attention is paid to locally ordered rare regions that are formed in the presence of quenched disorder even when the bulk system is still in the nonmagnetic phase. It is shown that these local moments or instantons destroy the previously found critical fixed point in the case of antiferromagnets. In the case of itinerant ferromagnets, the critical behavior is unaffected by the rare regions due to an effective long-range interaction between the order parameter fluctuations.