Cluster formation in quantum critical systems

TL;DR

This paper reviews evidence of magnetic cluster formation in quantum critical systems and discusses how clustering influences critical behavior and universality classes near phase transitions.

Contribution

It provides a comprehensive review of experimental evidence and theoretical implications of cluster formation in quantum critical systems, highlighting conditions affecting their impact.

Findings

Magnetic clusters are verified in various quantum critical systems.

Cluster formation affects the universality class near phase transitions.

Clustering influences the response of both doped and stoichiometric systems.

Abstract

The presence of magnetic clusters has been verified in both antiferromagnetic and ferromagnetic quantum critical systems. We review some of the strongest evidence for strongly doped quantum critical systems (Ce(Ru$_{0.24}$Fe$_{0.76}$)$_2$Ge$_2$) and we discuss the implications for the response of the system when cluster formation is combined with finite size effects. In particular, we discuss the change of universality class that is observed close to the order-disorder transition. We detail the conditions under which clustering effects will play a significant role also in the response of stoichiometric systems and their experimental signature.