495 research outputs found
Modulated electronic configurations in selectively doped multilayered nanostructures
A simple theoretical model is proposed to describe the recent experimental
results on formation of induced superconducting state and anomalous tunneling
characteristics in selectively doped multilayered nanostructures based on
LaCuO perovskite. In particular, it is shown that the structure
composed from the nominally non-superconducting (undoped and overdoped) layers
turns to be superconducting with superconductivity confined to narrow regions
near the interfaces, in agreement with the experimental observations.Comment: 4 pages, 4 figures, revte
Formation of d-wave superconducting order in a randomly doped lattice
We consider the interplay between superconducting coupling and dopant
impurity scattering of charge carriers in planar square lattice systems and
examine physical conditions (doping level, temperature, local symmetry of
coupling and scattering potentials) necessary in this model system to obtain a
d-wave superconducting order, like that observed in real doped cuprate HTSC
materials. Using the Lifshitz model for the disorder introduced into system by
dopants, we analyze also the non-uniform structure of such d-wave parameter,
including both its magnitude and phase variation. The results indicate that
d-wave superconductivity turns possible in a doped metal until it can be
destroyed at too high doping levels.Comment: 22 pages, 2 figure
Magnetoresistance of Highly Correlated Electron Liquid
The behavior in magnetic fields of a highly correlated electron liquid
approaching the fermion condensation quantum phase transition from the
disordered phase is considered. We show that at sufficiently high temperatures
the effective mass starts to depend on , . This dependence of the effective mass at elevated
temperatures leads to the non-Fermi liquid behavior of the resistivity,
and at higher temperatures . The
application of a magnetic field restores the common behavior of the
resistivity. The effective mass depends on the magnetic field, , being approximately independent of the temperature at . At , the dependence of the
effective mass is re-established. We demonstrate that this phase diagram
has a strong impact on the magnetoresistance (MR) of the highly correlated
electron liquid. The MR as a function of the temperature exhibits a transition
from the negative values of MR at to the positive values at . Thus, at , MR as a function of the temperature
possesses a node at .Comment: 7 pages, revtex, no figure
Mass Transfer Mechanism in Real Crystals by Pulsed Laser Irradiation
The dynamic processes in the surface layers of metals subjected activity of a
pulsing laser irradiation, which destroyed not the crystalline structure in
details surveyed. The procedure of calculation of a dislocation density
generated in bulk of metal during the relaxation processes and at repeated
pulse laser action is presented. The results of evaluations coincide with high
accuracy with transmission electron microscopy dates. The
dislocation-interstitial mechanism of laser-stimulated mass-transfer in real
crystals is presented on the basis of the ideas of the interaction of structure
defects in dynamically deforming medium. The good compliance of theoretical and
experimental results approves a defining role of the presented mechanism of
mass transfer at pulse laser action on metals. The possible implementation this
dislocation-interstitial mechanism of mass transfer in metals to other cases of
pulsing influences is justifiedComment: 10 pages, 2 figures, Late
Ground state instability in systems of strongly interacting fermions
We analyze stability of a fermion system with model repulsive pair
interaction potential. The possibility for different types of restructuring of
the Fermi ground state (at sufficiently great coupling constant) is related to
the analytic properties of such potential. In particular, for the screened
Coulomb law it is shown that the restructuring cannot be of the Fermi
condensation type, known earlier for some exactly solvable models, and instead
it belongs to the class of topological transitions (TT). For this model, a
phase diagram has been built in the variables "screening parameter - coupling
constant" which displays two kinds of TT: a 5/2-kind similar to the known
Lifshitz transitions in metals, and a 2-kind characteristic for a uniform
strongly interacting system.Comment: The article has 11 pages, in Latex 2e (from Lyx), 3 eps figures or a
ps fil
Universal Behavior of Heavy-Fermion Metals Near a Quantum Critical Point
The behavior of the electronic system of heavy fermion metals is considered.
We show that there exist at least two main types of the behavior when the
system is nearby a quantum critical point which can be identified as the
fermion condensation quantum phase transition (FCQPT). We show that the first
type is represented by the behavior of a highly correlated Fermi-liquid, while
the second type is depicted by the behavior of a strongly correlated
Fermi-liquid. If the system approaches FCQPT from the disordered phase, it can
be viewed as a highly correlated Fermi-liquid which at low temperatures
exhibits the behavior of Landau Fermi liquid (LFL). At higher temperatures ,
it demonstrates the non-Fermi liquid (NFL) behavior which can be converted into
the LFL behavior by the application of magnetic fields . If the system has
undergone FCQPT, it can be considered as a strongly correlated Fermi-liquid
which demonstrates the NFL behavior even at low temperatures. It can be turned
into LFL by applying magnetic fields . We show that the effective mass
diverges at the very point that the N\'eel temperature goes to zero. The
phase diagrams of both liquids are studied. We demonstrate that these
phase diagrams have a strong impact on the main properties of heavy-fermion
metals such as the magnetoresistance, resistivity, specific heat,
magnetization, volume thermal expansion, etc.Comment: Revtex, 11 pages, revised and accepted by JETP Let
Quasiparticles in the Superconducting State of High-T_c Metals
We consider the behavior of quasiparticles in the superconducting state of
high-T_c metals within the framework of the theory of superconducting state
based on the fermion condensation quantum phase transition. We show that the
behavior coincides with the behavior of Bogoliubov quasiparticles, whereas the
maximum value of the superconducting gap and other exotic properties are
determined by the presence of the fermion condensate. If at low temperatures
the normal state is recovered by the application of a magnetic field
suppressing the superconductivity, the induced state can be viewed as Landau
Fermi liquid. These observations are in good agreement with recent experimental
facts.Comment: 8 pages, Revte
Behavior of Fermi Systems Approaching Fermion Condensation Quantum Phase Transition from Disordered Phase
The behavior of Fermi systems which approach the fermion condensation quantum
phase transition (FCQPT) from the disordered phase is considered. We show that
the quasiparticle effective mass diverges as
where is the system density and is the critical point at which
FCQPT occurs. Such a behavior is of general form and takes place in both three
dimensional (3D) systems and two dimensional (2D) ones. Since the effective
mass is finite, the system exhibits the Landau Fermi liquid behavior. At
, the behavior can be viewed as a highly correlated
one, because the effective mass is large and strongly depends on the density.
In case of electronic systems the Wiedemann-Franz law is held and
Kadowaki-Woods ratio is preserved. Beyond the region ,
the effective mass is approximately constant and the system becomes
conventional Landau Fermi liquid.Comment: 9 pages, revtex, no figure
Influence of a low magnetic field on the thermal diffusivity of Bi-2212
The thermal diffusivity of a Bi-2212 polycrystalline sample has been measured
under a 1T magnetic field applied perpendicularly to the heat flux. The
magnetic contribution to the heat carrier mean free path has been extracted and
is found to behave as a simple power law. This behavior can be attributed to a
percolation process of electrons in the vortex lattice created by the magnetic
field.Comment: 10 pages, 3 figures; to be published in Phys. Rev.
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