Today I finished a review paper, together with John Mydosh from Leiden University, about quantum criticality in heavy fermion materials. It will be published (after editing and such) in the Handbook of Chemistry and Physics of Rare Earths and Actinides. Unfortunately, the Elsevier policies do not allow me to put it on arXiv, only on my personal webpage.
Abstract: In this Chapter we discuss quantum critically, the notion that properties of a material are governed by the existence of a phase transition at zero temperature. The point where a second-order (continuous) phase transition takes places is known as a quantum critical point (QCP). Materials that exhibit a quantum critical points can be tuned through their quantum phase transition by, for example, pressure, chemical doping or disorder, frustration, and magnetic field. The study of quantum phase transitions (QPT) was initially theoretically driven, showing that high- temperature properties of a material with a QPT are directly influenced by the properties of the QCP itself. We start this Chapter by discussing the predictions of quantum critical and Hertz- Millis theory. Experimentally, we will mainly limit ourselves to f-electron based materials: the rare-earths Li(Ho,Y)F4, Ce(Cu,Au)6, YbRh2Si2, the Cerium series Ce(Co, Rh; Ir)In5 and one actinide based material, URu2Si2. These ‘heavy fermion’ metals (4f or 5f) represent prototype materials of quantum critical matter, and we will critically review their experimental signatures and their evolving theoretical descriptions. We conclude with other manifestations of quantum phase transitions beyond the rare-earths and actinides.