Speaker
David Broun
(Simon Fraser University)
Description
In the so-called "heavy-fermion" metals, the hybridization of the conduction band with electrons localized in partially filled $f$ orbitals leads to the formation of heavy quasiparticles, for which the effective mass can be renormalized by a factor of 100 or more. However, the itinerant nature of these quasiparticles competes with a tendency to form more conventional, magnetically ordered states. These materials are therefore situated near a quantum critical point - a zero-temperature phase transition driven by the competition between kinetic energy and potential energy. This conflict between itinerancy and localization lies at the heart of all correlated electron materials, and makes heavy-fermion systems a model system for testing and understanding correlated quantum matter.
Along with the formation of ultra-heavy quasiparticles, the scattering dynamics in heavy fermion compounds also undergo a strong renormalization. This critical slowing-down brings important electronic timescales, such as electronic scattering rates, down into the GHz range, where optical-type measurements and analyses can be carried out with microwaves. We have developed a dilution-refrigerator-based system for carrying out these measurements, and have used it to study a range of heavy fermion materials such as CeCoIn5, UBe13 and URu2Si2. Following an overview of the relevant physics, I will present a summary of our most striking results, illustrating the critical slowing down and mass enhancement that accompany a quantum phase transition.
Author
David Broun
(Simon Fraser University)
