11,940 research outputs found
Atomic coherence and interference phenomena in resonant nonlinear optical interactions
Interference effects in quantum transitions, giving rise to amplification
without inversion, optical transparency and to enhancements in nonlinear
optical frequency conversions are considered. Review of the relevant early
theoretical and experimental results is given. The role of relaxation
processes, spontaneous cascade of polarizations, local field effects,
Doppler-broadening, as well as specific features of the interference in the
spectral continuum are discussed.Comment: 13 pages, 13 eps figures, review paper, Proceedings of the 15th
International Conference on Nonlinear Optics - ICONO'9
Asymmetric tunneling, Andreev reflection and dynamic conductance spectra in strongly correlated metals
Landau Fermi liquid theory predicts that the differential conductivity
between metallic point and metal is a symmetric function of voltage bias V.
This symmetry holds if the particle-hole symmetry is preserved. We show that
the situation can be different when one of the two metals is a strongly
correlated one whose electronic system can be represented by a heavy fermion
liquid. When the heavy fermion liquid undergoes fermion condensation quantum
phase transition, the particle-hole symmetry is violated making both the
differential tunneling conductivity and dynamic conductance asymmetric as a
function of applied voltage. This asymmetry can be observed when the strongly
correlated metal is either normal or superconducting. We show that at small
values of $V the asymmetric part of the dynamic conductance is a linear
function of V and inversely proportional to the maximum value of the gap and
does not depend on temperature provided that metal is superconducting, when it
becomes normal the asymmetric part diminishes at elevated temperatures.Comment: 8 pages, 7 figure
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
Scaling in Dynamic Susceptibility of Herbertsmithite and Heavy-Fermion Metals
We present a theory of the dynamic magnetic susceptibility of quantum spin
liquid. The obtained results are in good agreement with experimental facts
collected on herbertsmithite ZnCu3(OH)6Cl2 and on heavy-fermion metals, and
allow us to predict a new scaling in magnetic fields in the dynamic
susceptibility. Under the application of strong magnetic fields quantum spin
liquid becomes completely polarized. We show that this polarization can be
viewed as a manifestation of gapped excitations when investigating the
spin-lattice relaxation rate.Comment: 6 pages, 3 figures, minor improvements, published versio
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