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arXiv:cond-mat/0502292 · Europhysics Letters (EPL)

Thermodynamic properties of Fermi systems with flat single-particle spectra

V. A Khodel, J. W Clark, M. V Zverev

Published Sep 20, 2005• 9 citations
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Abstract

The behavior of strongly correlated Fermi systems is investigated beyond the onset of a phase transition where the single-particle spectrum ξ( p ) becomes flat. The Landau-Migdal quasiparticle picture is shown to remain applicable on the ordered side of this transition. Nevertheless, low-temperature properties evaluated within this picture show profound changes relative to results of Landau theory, as a direct consequence of the flattening of ξ( p ). Stability conditions for this class of systems are examined, and the nature of antiferromagnetic quantum phase transitions is elucidated.

DOI
10.1209/epl/i2005-10233-9

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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 ε(p)ε({\bf p})ε(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.
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.
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