526 research outputs found
Anisotropic Superconductivity in the Induced Pairing Model
The model of local electron pairs and itinerant fermions coupled via charge
exchange mechanism, which mutually induces superconductivity in both subsystems
is studied for anisotropic pairing symmetry. The phase diagram is presented and
the phase fluctuations effects are analyzed within the Kosterlitz-Thouless
scenario.Comment: 4 pages, 2 figures. Physica B (in press), Proceedings of the
International Conference on Strongly Correlated Electron Systems, Ann Arbor,
Michigan, August 6-10, 200
Phase transition between quantum and classical regimes for the escape rate of a biaxial spin system
Employing the method of mapping the spin problem onto a particle one, we have
derived the particle Hamiltonian for a biaxial spin system with a transverse or
longitudinal magnetic field. Using the Hamiltonian and introducing the
parameter where (U_{min})
corresponds to the top (bottom) of the potential and is the energy of the
particle, we have studied the first- or second-order transition around the
crossover temperature between thermal and quantum regimes for the escape rate,
depending on the anisotropy constant and the external magnetic field. It is
shown that the phase boundary separating the first- and second-order transition
and its crossover temperature are greatly influenced by the transverse
anisotropy constant as well as the transverse or longitudinal magnetic field.Comment: 5 pages + 3 figures, to be published in Phys. Rev.
Interaction of Charged 3D Soliton with Coulomb Center
The Einstein - de Broglie particle-soliton concept is applied to simulate
stationary states of an electron in a hydrogen atom. According to this concept,
the electron is described by the localized regular solutions to some nonlinear
equations. In the framework of Synge model for interacting scalar and
electromagnetic fields a system of integral equations has been obtained, which
describes the interaction between charged 3D soliton and Coulomb center. The
asymptotic expressions for physical fields, describing soliton moving around
the fixed Coulomb center, have been obtained with the help of integral
equations. It is shown that the electron-soliton center travels along some
stationary orbit around the Coulomb center. The electromagnetic radiation is
absent as the Poynting vector has non-wave asymptote after
averaging over angles, i.e. the existence of spherical surface corresponding to
null Poynting vector stream, has been proved. Vector lines for Poynting vector
are constructed in asymptotical area.Comment: LaTeX ,12 page
Sugarbeet Production Under Reduced Tillage Prospects And Problems
A study was initiated in the fall of 1977 to obtain base line data on the applicability of reduced tillage sugarbeet production in the Red River Valley. Three reduced tillage systems were compared to a conventional system which consisted of fall plow plus secondary tillage. Results indicated warmer early spring soil temperatures, better seedling emergence, lower ground-level wind speed and no significant yield loss under reduced tillage as compared to the conventional system
Tunnelling series in terms of perturbation theory for quantum spin systems
Considered is quantum tunnelling in anisotropic spin systems in a magnetic
field perpendicular to the anisotropy axis. In the domain of small field the
problem of calculating tunnelling splitting of energy levels is reduced to
constructing the perturbatio n series with degeneracy, the order of degeneracy
being proportional to a spin value. Partial summation of this series taking
into account ''dangerous terms'' with small denominators is performed and the
value of tunnelling splitting is calculated with allowance for the first
correction with respect to a magnetic field.Comment: 7 pages, REVTeX 3.
Unusual condensates in quark and atomic systems
In these lectures we discuss condensates which are formed in quark matter
when it is squeezed and in a gas of fermionic atoms when it is cooled. The
behavior of these two seemingly very different systems reveals striking
similarities. In particular, in both systems the Bose-Einstein condensate to
Bardeen--Cooper-Schrieffer (BEC-BCS) crossover takes place.Comment: Lectures delivered at 8th Moscow school of Physics (33rd ITEP Winter
School of Physics
Macroscopic Quantum Coherence in Small Antiferromagnetic Particle and the Quantum Interference Effects
Starting from the Hamiltonian operator of the noncompensated two-sublattice
model of a small antiferromagnetic particle, we derive the effective Lagrangian
of a biaxial antiferromagnetic particle in an external magnetic field with the
help of spin-coherent-state path integrals. Two unequal level-shifts induced by
tunneling through two types of barriers are obtained using the instanton
method. The energy spectrum is found from Bloch theory regarding the periodic
potential as a superlattice. The external magnetic field indeed removes
Kramers' degeneracy, however a new quenching of the energy splitting depending
on the applied magnetic field is observed for both integer and half-integer
spins due to the quantum interference between transitions through two types of
barriers.Comment: 9 pages, Latex, 4 Postscript figure
Macroscopic quantum coherence in mesoscopic ferromagnetic systems
In this paper we study the Macroscopic Quantum Oscillation (MQO) effect in
ferromagnetic single domain magnets with a magnetic field applied along the
hard anistropy axis. The level splitting for the ground state, derived with the
conventional instanton method, oscillates with the external field and is
quenched at some field values. A formula for quantum tunneling at excited
levels is also obtained. The existence of topological phase accounts for this
kind of oscillation and the corresponding thermodynamical quantities exhibit
similar interference effects which resembles to some extent the electron
quantum phase interference induced by gauge potential in the Aharonov-Bohm
effect and the -vacuum in Yang-Mills field theory..Comment: 12 pages, 4 figures, to appear in Phys. Rev.
Quantum Phase Interference for Quantum Tunneling in Spin Systems
The point-particle-like Hamiltonian of a biaxial spin particle with external
magnetic field along the hard axis is obtained in terms of the potential field
description of spin systems with exact spin-coordinate correspondence. The
Zeeman energy term turns out to be an effective gauge potential which leads to
a nonintegrable pha se of the Euclidean Feynman propagator.
The phase interference between clockwise and anticlockwise under barrier
propagations is recognized explicitly as the Aharonov-Bohm effect. An
additional phase which is significant for quantum phase interference is
discovered with the quantum theory of spin systems besides the known phase
obtained with the semiclassical treatment of spin. We also show the energ y
dependence of the effect and obtain the tunneling splitting at excited states
with the help of periodic instantons.Comment: 19 pages, no figure, to appear in PR
Quantum-Classical Phase Transition of Escape rate in Biaxial Spin Particles
The escape rates of the biaxial single domain spin particles with and without
an applied magnetic field are investigated. Using the strict potential field
description of spin systems developed by Ulyanov and Zaslavskii we obtain new
effective Hamiltonians which are considered to be in exact spin-coordinate
correspondence unlike the well studied effective Hamiltonians with the
approximate correspondence. The sharp first-order transition is found in both
cases. The phase diagram of the transitions depending on the anisotropy
constant and the external field is also given.Comment: 15 pages, 8 figure
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