Quantum Criticality in Heavy Electron Compounds

Abstract

Heavy electron systems provide ideal venues to study a range of issues associated with quantum criticality, including unconventional electronic phases, moment formation, and complex phase diagrams with exotic critical phenomena. In the heavy electron antiferromagnets studied so far, magnetic order occurs via a second order phase transition which can be tuned via pressure or field to a quantum critical point. Fermi liquid behavior is found beyond the quantum critical point, and the quasiparticle mass diverges at the quantum critical point, nucleating the moments required to enable magnetic order itself. We review here our experimental results on a new heavy electron system, Yb3Pt4, where antiferromagnetic order is weakly first order in zero field, but becomes second order at a critical endpoint with the application of magnetic field. No divergence of the quasiparticle mass is observed near the quantum critical field, and instead magnetic order is driven by the exchange enhancement of the Fermi liquid itself. These data support the thesis that there are multiple routes to quantum criticality in the heavy electron compounds.