Absence of conventional quantum phase transitions in itinerant systems with disorder

TL;DR

This paper investigates how disorder affects quantum critical points in itinerant systems, revealing that spin fluctuations induce non-Ohmic dissipation, which prevents Griffiths phases and leads to a cluster glass phase.

Contribution

It demonstrates that disorder-induced spin fluctuations destabilize Griffiths phases, resulting in a new cluster glass phase in itinerant quantum systems.

Findings

Disorder causes non-Ohmic dissipation via spin fluctuations.

Quantum Griffiths phases are destabilized by this dissipation.

A cluster glass phase forms before uniform magnetic ordering.

Abstract

Effects of disorder are examined in itinerant systems close to quantum critical points. We argue that spin fluctuations associated with the long-range part of the RKKY interactions generically induce non-Ohmic dissipation due to rare disorder configurations. This dissipative mechanism is found to destabilize quantum Griffiths phase behavior in itinerant systems with arbitrary symmetry of the order parameter, leading to the formation of a "cluster glass" phase preceding uniform ordering.