1,134 research outputs found
Fermion condensation: a strange idea successfully explaining behavior of numerous objects in Nature
Strongly correlated Fermi systems are among the most intriguing, best
experimentally studied and fundamental systems in physics. These are, however,
in defiance of theoretical understanding. The ideas based on the concepts like
Kondo lattice and involving quantum and thermal fluctuations at a quantum
critical point have been used to explain the unusual physics. Alas, being
suggested to describe one property, these approaches fail to explain the
others. This means a real crisis in theory suggesting that there is a hidden
fundamental law of nature, which remains to be recognized. A theory of fermion
condensation quantum phase transition, preserving the extended quasiparticles
paradigm and intimately related to unlimited growth of the effective mass as a
function of temperature, magnetic field etc, is capable to resolve the problem.
We discuss the construction of the theory and show that it delivers theoretical
explanations of vast majority of experimental results in strongly correlated
systems such as heavy-fermion metals and quasi-two-dimensional Fermi systems.Comment: 12 pages, 14 figures, Invited talk at Bogolyubov Kyiv Conference,
Modern Problems of Theoretical and Mathematical Physics, 2009, Kyiv, Ukrain
Scaling Behavior of Heavy Fermion Metals
Strongly correlated Fermi systems are fundamental systems in physics that are
best studied experimentally, which until very recently have lacked theoretical
explanations. This review discusses the construction of a theory and the
analysis of phenomena occurring in strongly correlated Fermi systems such as
heavy-fermion (HF) metals and two-dimensional (2D) Fermi systems. It is shown
that the basic properties and the scaling behavior of HF metals can be
described within the framework of a fermion condensation quantum phase
transition (FCQPT) and extended quasiparticle paradigm that allow us to explain
the non-Fermi liquid behavior observed in strongly correlated Fermi systems. In
contrast to the Landau paradigm stating that the quasiparticle effective mass
is a constant, the effective mass of new quasiparticles strongly depends on
temperature, magnetic field, pressure, and other parameters. Having analyzed
collected facts on strongly correlated Fermi systems with quite different
microscopic nature, we find these to exhibit the same non-Fermi liquid behavior
at FCQPT. We show both analytically and using arguments based entirely on the
experimental grounds that the data collected on very different strongly
correlated Fermi systems have a universal scaling behavior, and materials with
strongly correlated fermions can unexpectedly be uniform in their diversity.
Our analysis of strongly correlated systems such as HF metals and 2D Fermi
systems is in the context of salient experimental results. Our calculations of
the non-Fermi liquid behavior, the scales and thermodynamic, relaxation and
transport properties are in good agreement with experimental facts.Comment: 100 pages, 66 figures, to appear in Physics Report
Inversionless gain in a three-level system driven by a strong field and collisions
Inversionless gain in a three-level system driven by a strong external field
and by collisions with a buffer gas is investigated. The mechanism of
populating of the upper laser level contributed by the collision transfer as
well as by relaxation caused by a buffer gas is discussed in detail. Explicit
formulae for analysis of optimal conditions are derived. The mechanism
developed here for the incoherent pump could be generalized to other systems.Comment: RevTeX, 9 pages, 4 eps figure
Explicit Non-Abelian Monopoles and Instantons in SU(N) Pure Yang-Mills Theory
It is well known that there are no static non-Abelian monopole solutions in
pure Yang-Mills theory on Minkowski space R^{3,1}. We show that such solutions
exist in SU(N) gauge theory on the spaces R^2\times S^2 and R^1\times S^1\times
S^2 with Minkowski signature (-+++). In the temporal gauge they are solutions
of pure Yang-Mills theory on T^1\times S^2, where T^1 is R^1 or S^1. Namely,
imposing SO(3)-invariance and some reality conditions, we consistently reduce
the Yang-Mills model on the above spaces to a non-Abelian analog of the \phi^4
kink model whose static solutions give SU(N) monopole (-antimonopole)
configurations on the space R^{1,1}\times S^2 via the above-mentioned
correspondence. These solutions can also be considered as instanton
configurations of Yang-Mills theory in 2+1 dimensions. The kink model on
R^1\times S^1 admits also periodic sphaleron-type solutions describing chains
of n kink-antikink pairs spaced around the circle S^1 with arbitrary n>0. They
correspond to chains of n static monopole-antimonopole pairs on the space
R^1\times S^1\times S^2 which can also be interpreted as instanton
configurations in 2+1 dimensional pure Yang-Mills theory at finite temperature
(thermal time circle). We also describe similar solutions in Euclidean SU(N)
gauge theory on S^1\times S^3 interpreted as chains of n
instanton-antiinstanton pairs.Comment: 16 pages; v2: subsection on topological charges added, title
expanded, some coefficients corrected, version to appear in PR
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