Low energy excitations of highly correlated electron systems

Recent studies of properties of heavy quasiparticles have helped to establish that f electrons and conduction electrons in the normal states of certain U and Ce compounds are characterized by Fermi volumes consistent with Luttingeris Theorem and by integrated quasiparticle masses which agree with measured linear coefficients of the specific heat. Evidence is presented that this Fermi Liquid picture may, however, break down when the ground state is near pressure or magnetic field induced phase transitions.