51 research outputs found
On the possibility to consider fullerene shell C60 as a conducting sphere
Correctness of the model representing the fullerene shell C60 as a conducting
sphere has been analyzed. The static and dynamical polarizabilities of the
molecule C60 have been calculated on the basis of experimental data on the
photo-absorption cross- section of fullerene. It has been shown that the real
C60 in the static electric field behaves most likely as a set of separate
carbon atoms rather than as a conducting sphere and its static polarizability
exceeds by more than two times that of conducting sphere.Comment: 5 pages, 2 figure
Atomic Bremsstrahlung: retrospectives, current status and perspectives
We describe here the Atomic bremsstrahlung - emission of continuous spectrum
electromagnetic radiation, which is generated in collisions of particles that
have internal deformable structure that includes positively and negatively
charged constituents. The deformation of one of or both colliding partners
induces multiple, mainly dipole, time-dependent electrical moments that become
a source of radiation. The history of Atomic bremsstrahlung invention is
presented and it's unusual in comparison to ordinary bremsstrahlung properties
are discussed. As examples, fast electron - atom, non-relativistic and
relativistic collisions are considered. Attention is given to ion - atom and
atom - atom collisions. Specifics of elastic and inelastic (i.e. radiation
accompanied by destruction of collision partners) Atomic bremsstrahlung will be
mentioned. Attention will be given to possible manifestation of Atomic
bremsstrahlung in Nature and in some exotic systems, for instance scattering of
electrons upon muonic hydrogen. Some cooperative effects connected to Atomic
bremsstrahlung will be considered. New classical schemes similar to Atomic
bremsstrahlung will be presented.Comment: 29 pages, 11 figures Submitted to Electron spectroscopy and the
related phenomen
Slow long-range decay of bound Hartree-Fock orbitals and enhancement of the exchange interaction and tunneling
Exchange interaction strongly influences the long-range behaviour of
localised electron orbitals. It violates the oscillation theorem (creates extra
nodes) and produces a power-law decay instead of the usual exponential decrease
at large distances. For inner orbitals inside molecules decay is 1/r^2, for
macroscopic systems cos(k_f r)/r^n, where k_f is the Fermi momentum and n=3 for
1D, n=3.5 for 2D and n=4 for 3D crystal. Slow decay increases the exchange
interaction between localised spins and the under-barrier tunneling
amplitude.The under-barrier transmission coefficients in solids (e.g. for point
contacts) become temperature-dependent
Trapped Atomic Fermi Gases
A many-body system of fermion atoms with a model interaction characterized by
the scattering length is considered. We treat both and the density as
parameters assuming that the system can be created artificially in a trap. If
is negative the system becomes strongly correlated at densities , provided the scattering length is the dominant parameter of the
problem. It means that we consider to be much bigger than the radius of
the interaction or any other relevant parameter of the system. The density
at which the compressibility vanishes is defined by . Thus, a system composed of fermion atoms with the scattering length
is completely unstable at low densities, inevitably collapsing
until the repulsive core stops the density growth. As a result, any Fermi
system possesses the equilibrium density and energy if the bare
particle-particle interaction is sufficiently strong to make negative and
to be the dominant parameter. This behavior can be realized in a trap. Our
results show that a low density neutron matter can have the equilibrium
density.Comment: 6 pages, to be published in Physics Letters
Relationships between the superconducting gap, pseudogap and transition temperature in High-T_c superconductors
The crossover from superconducting gap to pseudogap is considered. We show
that the superconductivity is destroyed at the temperature , with the
superconducting gap being smoothly transformed into the pseudogap. Relations,
which are of general interest, between the maximum values of the gap
, and are established. We presents arguments that
as a function of the doping level is approximately a straight line that
crosses the abscissa at some point . In the vicinity of this point
coincides with , and at the fermion condensation quantum
phase transition takes place.Comment: 8 pages, Revtex, 1 figure; Slightly revised version, some references
are adde
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 the unlimited growth of the effective mass as a function of the 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 the vast majority of experimental results in strongly correlated systems such as heavy-fermion metals and quasi-two-dimensional Fermi systems. Our analysis is placed in the context of recent salient experimental results. Our calculations of the non-Fermi liquid behavior, the scales, and thermodynamic and transport properties are in good agreement with the heat capacity, magnetization, longitudinal magnetoresistance, and magnetic entropy obtained in remarkable measurements on the heavy-fermion metal YbRh2Si2. Using two-dimensional 3He as an example, we demonstrate that the main universal features of its experimental temperature T - density x phase diagram resemble those of the heavy-fermion metals. We propose a simple expression for the effective mass, describing all diverse experimental facts on the 3He in the unified manner and demonstrating that the universal behavior of the effective mass coincides with that observed in heavy-fermion metals.Сильнокорельованi фермi-системи є найбiльш фiзично загадковими фундаментальними та добре вивченими експериментально системами, за вiдсутностi, у той же час, їх теоретичного опису. Iдеї, якi ґрунтуються на ґратцi Кондо та квантових i термiчних флуктуацiях, використовуються для пояснення незвичної фiзики. Однак, будучи запропонованими для пояснення однiєї властивостi, цi iдеї виявилися некорисними для пояснення iнших властивостей. Такий стан речей вказує на сучасну кризу теорiї, для подолання якої нам треба буде вiдкрити невiдомий поки що фундаментальний закон. Теорiя фермiонконденсатного фазового квантового переходу, яка пiдтримує розширену парадигму квазiчастинок i допускає необмежене зростання ефективної маси як функцiї температури та напруженостi магнiтного поля, має змогу вирiшити проблему сильнокорельованих систем. Обговорено побудову теорiї i показано, що вона дозволяє описати широке коло експериментальних даних в областi таких сильнокорельованих систем, як метали з важкими фермiонами та двовимiрнi фермi-системи. Наш розгляд включає в себе опис вартих уваги експериментiв. Проведенi обчислення нефермi-рiдинної поведiнки, термодинамiчних i транспортних властивостей та вiдповiдних енергетичних шкал добре узгоджуються з даними. Цi данi вимiру теплоємностi, намагнiченостi, поздовжнього магнетоопору i магнiтної ентропiї одержано в унiкальних вимiрах на металi з важкими фермiонами YbRh2Si2. Продемонстровано, що основнi унiверсальнi властивостi фазової дiаграми температура–густина двовимiрного 3He збiгається з вiдповiдними властивостями металiв iз важкими фермiонами. Запропоновано просту формулу для ефективної маси, яка дозволяє описати унiверсальнi властивостi сильнокорельованих систем i пояснити рiзноманiтнi експериментальнi данi, зiбранi у вимiрах на 3He i металах з важкими фермiонами
On the relation between the Hartree-Fock and Kohn-Sham approaches
We show that the Hartree-Fock (HF) results cannot be reproduced within the
framework of Kohn-Sham (KS) theory because the single-particle densities of
finite systems obtained within the HF calculations are not -representable,
i.e., do not correspond to any ground state of a non-interacting electron
systems in a local external potential. For this reason, the KS theory, which
finds a minimum on a different subset of all densities, can overestimate the
ground state energy, as compared to the HF result. The discrepancy between the
two approaches provides no grounds to assume that either the KS theory or the
density functional theory suffers from internal contradictions.Comment: 7 pages, ReVtex, revised and accepted by Physics Letters
Quasiparticle picture of high temperature superconductors in the frame of Fermi liquid with the fermion condensate
A model of a Fermi liquid with the fermion condensate (FC) is applied to the
consideration of quasiparticle excitations in high temperature superconductors,
in their superconducting and normal states. Within our model the appearance of
the fermion condensate presents a quantum phase transition, that separates the
regions of normal and strongly correlated electron liquids. Beyond the phase
transition point the quasiparticle system is divided into two subsystems, one
containing normal quasiparticles and the other --- fermion condensate localized
at the Fermi surface and characterized by almost dispersionless single-particle
excitations. In the superconducting state the quasiparticle dispersion in
systems with FC can be presented by two straight lines, characterized by
effective masses and , respectively, and intersecting near
the binding energy which is of the order of the superconducting gap. This same
quasiparticle picture persists in the normal state, thus manifesting itself
over a wide range of temperatures as new energy scales. Arguments are presented
that fermion systems with FC have features of a quantum protectorate.Comment: 12 pages, Late
Neutron matter with a model interaction
An infinite system of neutrons interacting by a model pair potential is
considered. We investigate a case when this potential is sufficiently strong
attractive, so that its scattering length tends to infinity. It appeared, that
if the structure of the potential is simple enough, including no finite
parameters, reliable evidences can be presented that such a system is
completely unstable at any finite density. The incompressibility as a function
of the density is negative, reaching zero value when the density tends to zero.
If the potential contains a sufficiently strong repulsive core then the system
possesses an equilibrium density. The main features of a theory describing such
systems are considered.Comment: 8 pages, LaTeX. In press, Eur. Phys. J.
Energy scales and magnetoresistance at a quantum critical point
The magnetoresistance (MR) of CeCoIn_5 is notably different from that in many
conventional metals. We show that a pronounced crossover from negative to
positive MR at elevated temperatures and fixed magnetic fields is determined by
the scaling behavior of quasiparticle effective mass. At a quantum critical
point (QCP) this dependence generates kinks (crossover points from fast to slow
growth) in thermodynamic characteristics (like specific heat, magnetization
etc) at some temperatures when a strongly correlated electron system transits
from the magnetic field induced Landau Fermi liquid (LFL) regime to the
non-Fermi liquid (NFL) one taking place at rising temperatures. We show that
the above kink-like peculiarity separates two distinct energy scales in QCP
vicinity - low temperature LFL scale and high temperature one related to NFL
regime. Our comprehensive theoretical analysis of experimental data permits to
reveal for the first time new MR and kinks scaling behavior as well as to
identify the physical reasons for above energy scales.Comment: 7 pages, 6 figure
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