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 $a$ is considered. We treat both $a$ and the density as parameters assuming that the system can be created artificially in a trap. If $a$ is negative the system becomes strongly correlated at densities $\rho \sim |a|^{-3}$, provided the scattering length is the dominant parameter of the problem. It means that we consider $|a|$ to be much bigger than the radius of the interaction or any other relevant parameter of the system. The density $\rho_{c1}$ at which the compressibility vanishes is defined by $\rho_{c1}\sim |a|^{-3}$. Thus, a system composed of fermion atoms with the scattering length $a\to -\infty$ 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 $a$ 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 $T_c$, with the superconducting gap being smoothly transformed into the pseudogap. Relations, which are of general interest, between the maximum values of the gap $\Delta_1$, $T_c$ and $T^*$ are established. We presents arguments that $T^*$ as a function of the doping level $x$ is approximately a straight line that crosses the abscissa at some point $x_{FC}$. In the vicinity of this point $T^*$ coincides with $T_c$, and at $x=x_{FC}$ 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 $v$-representable, i.e., do not correspond to any ground state of a $N$ 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 $M^*_{FC}$ and $M^*_L$, 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