Quantum Critical Behavior of the Cluster Glass Phase

TL;DR

This paper investigates the quantum critical behavior of the cluster glass phase in disordered itinerant magnets, revealing a fluctuation-induced first-order transition at zero temperature due to quantum Griffiths effects.

Contribution

It demonstrates that quantum Griffiths anomalies cause a first-order transition at T=0 in systems with continuous symmetry, a novel insight into quantum criticality in disordered magnets.

Findings

Quantum Griffiths anomalies induce a first-order transition at T=0.

At higher temperatures, a conventional continuous transition is observed.

Enhanced non-Ohmic dissipation is a key factor in this behavior.

Abstract

In disordered itinerant magnets with arbitrary symmetry of the order parameter, the conventional quantum critical point between the ordered phase and the paramagnetic Fermi-liquid (PMFL) is destroyed due to the formation of an intervening cluster glass (CG) phase. In this Letter we discuss the quantum critical behavior at the CG-PMFL transition for systems with continuous symmetry. We show that fluctuations due to quantum Griffiths anomalies induce a first-order transition from the PMFL at T=0, while at higher temperatures a conventional continuous transition is restored. This behavior is a generic consequence of enhanced non-Ohmic dissipation caused by a broad distribution of energy scales within any quantum Griffiths phase in itinerant systems.