Quantum Criticality and Global Phase Diagram of Magnetic Heavy Fermions

TL;DR

This paper explores quantum critical points in heavy fermion metals, highlighting local and standard antiferromagnetic quantum criticality, and presents a global phase diagram based on experimental and theoretical insights.

Contribution

It introduces a comprehensive global phase diagram for magnetic heavy fermions, incorporating local quantum critical points and their implications for Fermi surface changes.

Findings

Identification of local quantum critical points involving Kondo breakdown

Observation of Fermi surface collapse at quantum critical points

Experimental support for the global phase diagram in heavy fermion systems

Abstract

Quantum criticality describes the collective fluctuations of matter undergoing a second-order phase transition at zero temperature. It is being discussed in a number of strongly correlated electron systems. A prototype case occurs in the heavy fermion metals, in which antiferromagnetic quantum critical points have been explicitly observed. Here, I address two types of antiferromagnetic quantum critical points. In addition to the standard description based on the fluctuations of the antiferromagnetic order, a local quantum critical point is also considered. It contains inherently quantum modes that are associated with a critical breakdown of the Kondo effect. Across such a quantum critical point, there is a sudden collapse of a large Fermi surface to a small one. I also consider the proximate antiferromagnetic and paramagnetic phases, and these considerations lead to a global phase diagram. Finally, I discuss the pertinent experiments on the antiferromagnetic heavy fermions, briefly address the case of ferromagnetic heavy fermions, and outline some directions for future studies.