Entropy excess in strongly correlated Fermi systems near a quantum critical point

Journal Article · Sat Dec 15 00:00:00 EST 2012 · Annals of Physics (New York)

DOI:https://doi.org/10.1016/J.AOP.2012.08.006· OSTI ID:22157021

Zverev, M. V. ^[1]; Khodel, V. A. ^[1]

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1. Russian Research Centre Kurchatov Institute, Moscow, 123182 (Russian Federation)

A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau quasiparticle theory to strongly correlated Fermi systems. Black-Right-Pointing-Pointer Analysis of associated topological phase transitions at a quantum critical point. Black-Right-Pointing-Pointer Fermi surface rearrangement featuring hole pockets or emergence of flat bands. Black-Right-Pointing-Pointer Shedding of flat-band excess entropy via pairing transition at very low temperature.

• OSTI ID: 22157021
• Journal Information: Annals of Physics (New York), Vol. 327, Issue 12; Other Information: Copyright (c) 2012 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-4916
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COOPER PAIRS
COUPLING
EFFECTIVE MASS
ELECTRON CORRELATION
ENERGY SPECTRA
ENTROPY
FERMI GAS
FERMI LEVEL
FERMIONS
GROUND STATES
HOLES
MOMENTUM TRANSFER
NERNST HEAT THEOREM
PHASE TRANSFORMATIONS
QUASI PARTICLES
TEMPERATURE DEPENDENCE
TEMPERATURE ZERO K
TOPOLOGY
VARIATIONAL METHODS