Session 1-1

Abstract

A quantum critical point (QCP) is defined as a continuous transition at absolute zero temperature (T) between an ordered phase, such as magnetic order which is the focus in this talk, and a disordered (paramagnetic) phase. The discovery and understanding of such QCPs have become one of the primary organizing principles for seeking new multifunctional states in quantum materials, ranging from bilayer graphene[1] to plutonium,[2] as well as applications for future quantum-information science technologies.[3] The theoretical understanding of QCPs, however, is limited to two different groups of models with distinctly different predictions for the nature of "quantum-critical fluctuations" that proliferate to finite T above a QCP.[4-6] Understanding those fluctuations is key for interpreting the origin of new ordered states that might emerge from them. An outstanding question for many QCPs, and f-electron materials with their disorder-free nature in particular, is what is the “universality class” and the physical mechanism(s) of the quantum-critical fluctuations that determine the electronic properties around the QCP,[7] and how they couple, if at all, to local charge degrees-of-freedom.[8] The recent discovery of an extremely rare example of clean ferromagnetic QCPs in ultra-high-quality cerium- and uranium-based f-electron materials[9,10] has attracted great attention and offers an exceptional opportunity to test controversial theoretical predictions and resolve speculation specific to the quantum criticality in these materials. In this talk, we will present our recent microscopic studies on a disorder-free f-electron ferromagnet that undergoes a quantum phase transition under applied pressure using nuclear magnetic resonance (NMR) and quadrupole resonance (NQR) techniques. The nature of local magnetism of 4f-moments at Cerium ions will be investigated and discussed in relation to various frameworks of QCPs predicted for this specific compound.