FORMATION OF HEAVY-FERMION STATES IN NON-FERMI-LIQUID IMPURITY SYSTEMS
Manakova L.A.

Received: July 6, 2000

PACS: 72.10.Fk, 72.15.Qm, 73.20.-r

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A mechanism for the occurrence of heavy-fermion states in non-Fermi-liquid (NFL) metals with f-shell impurities is proposed. The impurity with an unstable valency is suggested to have the energy spectrum consisting of a deep f-level and quasicontinuum states (narrow band) in resonance with the Fermi energy. Depending on the impurity concentration, the single-site NFL states are generated by the two-channel Kondo scattering for the low concentration (the «Kondo regime») or by the screening interaction for a relatively high concentration (the «X-ray edge regime»). It is shown that the NFL states are unstable against the scattering of the NFL excitations by electron states of the narrow band. This scattering generates additional narrow Fermi-liquid (FL) resonances at/near the Fermi level in the «Kondo regime» and in the «X-ray edge regime». The mixed-valence states are shown to be induced by new FL resonances. The mixed valency mechanism is local and is related to the instability of single-site NFL states. The FL resonances lead to the existence of additional energy scales and of pseudogaps near the Fermi level in the mixed-valence states. They also considerably narrow the region with a nearly integer valency.