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arXiv:cond-mat/0308309 · Physics of Atomic Nuclei

Spin degrees of freedom and flattening of the spectra of single-particle excitations in strongly correlated Fermi systems

V. A. Khodel, Peter Schuck, M. V. Zverev

Published Oct 1, 2003• 2 citations
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Abstract

The impact of long-range spin-spin correlations on the structure of a flat portion in single-particle spectra ξ ( p ), which emerges beyond the point where the Landau state loses its stability, is studied. We supplement the well-known Nozieres model of a Fermi system with limited scalar long-range forces by a similar long-range spin-dependent term and calculate the spectra versus its strength g . It is found that Nozieres' results hold as long as g >0. However, with g changing its sign, the spontaneous magnetization is shown to arise at any nonzero g . The increase in the strength | g | is demonstrated to result in shrinkage of the domain in momentum space, occupied by the flat portion of ξ ( p ), and, eventually, in its vanishing.

DOI
10.1134/1.1619498

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Non-Fermi liquid behavior of strongly correlated Fermi systems is derived within the Landau approach. We attribute this behavior to a phase transition associated with a rearrangement of the Landau state that leads to flattening of a portion of the single-particle spectrum ∊(p) in the vicinity of the Fermi surface. We demonstrate that the quasiparticle subsystem responsible for the flat spectrum possesses the same thermodynamic properties as a gas of localized spins. Theoretical results compare favorably with available experimental data. While departing radically from prevalent views on the origin of non-Fermi-liquid behavior, the theory advanced here is nevertheless a conservative one of in continuing to operate within the general framework of Landau theory.
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A quasiparticle pattern advanced in Landau’s first article on Fermi-liquid theory is adapted to elucidate the properties of a class of strongly correlated Fermi systems characterized by a Lifshitz phase diagram featuring a quantum critical point (QCP) where the density of states diverges. The necessary condition for stability of the Landau Fermi-Liquid state is shown to break down in such systems, triggering a cascade of topological phase transitions that lead, without symmetry violation, to states with multi-connected Fermi surfaces. The end point of this evolution is found to be an exceptional state whose spectrum of single-particle excitations exhibits a completely flat portion at zero temperature. Analysis of the evolution of the temperature dependence of the single-particle spectrum yields results that provide a natural explanation of classical behavior of this class of Fermi systems in the QCP region.