Quasi-particles in heavy fermion systems

Abstract

This article attempts to review our present understanding of nearly-independent-particle excitations—quasiparticles—in heavy fermion systems. The emphasis is on a realistic, that is material-specific, description of the highly correlated Fermi liquid state which develops at low temperatures. After an initial discussion of Landau's Fermi liquid theory and its application to metals the concept of renormalized band structure calculation is introduced. The fundamental ideas are considered and explicit prescriptions are derived which allow a phenomenological account to be made of the strong local correlations. A comparison is made between the calculated quasiparticle bands and the detailed information now available from Fermi surface studies. Next, the interaction among the quasiparticles is discussed with particular reference to its influence on the electronic compressibility and the spin susceptibility. The correlation-related contribution to the quasiparticle-phonon coupling is derived. The question of quasiparticle collisions is also briefly discussed. Finally, a brief review is given of ideas and theoretical models which are used to describe superconductivity in heavy fermion compounds; in this context, a concept for constructing realistic order parameters is explored which accounts for the lattice structure and the anisotropy of the Fermi surface.