Global magnetic phase diagram and local quantum criticality in heavy fermion metals

We address the global magnetic phase diagram of Kondo lattice systems. Through the distinct Fermi surface properties of the various phases at zero temperature, we argue that the phase diagram supports two quantum critical point (QCP) classes. One of these describes a direct transition from a magnetic metal phase with localized f-electrons to a paramagnetic one with itinerant f-electrons. This result provides the context for the picture of local quantum criticality, in which the Fermi surface jumps across the QCP and the quasiparticle residue vanishes as the QCP is approached from either side. Some of the unusual experiments, concerning the phases and QCPs of heavy fermion metals, are discussed from the present perspective. These developments have implications in broader contexts. In particular, they form a part of the growing evidence for quantum criticality that goes beyond the orthodox description in terms of order-parameter fluctuations.