Quantum Griffiths effects and smeared phase transitions in metals: theory and experiment

TL;DR

This paper reviews theoretical and experimental insights into rare region effects like Griffiths singularities and smeared transitions in disordered metals at quantum phase transitions, highlighting their impact on phase diagrams and observable behaviors.

Contribution

It provides a comprehensive overview of rare region phenomena in disordered metals, integrating recent experimental findings with theoretical frameworks.

Findings

Identification of quantum Griffiths singularities in experiments

Observation of smeared phase transitions in metallic systems

Analysis of phase diagrams influenced by rare regions

Abstract

In this paper, we review theoretical and experimental research on rare region effects at quantum phase transitions in disordered itinerant electron systems. After summarizing a few basic concepts about phase transitions in the presence of quenched randomness, we introduce the idea of rare regions and discuss their importance. We then analyze in detail the different phenomena that can arise at magnetic quantum phase transitions in disordered metals, including quantum Griffiths singularities, smeared phase transitions, and cluster-glass formation. For each scenario, we discuss the resulting phase diagram and summarize the behavior of various observables. We then review several recent experiments that provide examples of these rare region phenomena. We conclude by discussing limitations of current approaches and open questions.