13 research outputs found
A variational approach to the QCD wave functional:Dynamical mass generation and confinement
We perform a variational calculation in the SU(N) Yang Mills theory in 3+1
dimensions. Our trial variational states are explicitly gauge invariant, and
reduce to simple Gaussian states in the zero coupling limit. Our main result is
that the energy is minimized for the value of the variational parameter away
form the perturbative value. The best variational state is therefore
characterized by a dynamically generated mass scale . This scale is related
to the perturbative scale by the following relation:
. Taking the one loop QCD -
function and we find (for N=3) the vacuum condensate
.Comment: 37 pages, (1 Figure available upon request), preprint LA-UR-94-2727,
PUPT-149
Does theory of quantum correction to conductivity agree with experimental data in 2D systems?
The quantum correction to the conductivity have been studied in two types of
2D heterostructures: with doped quantum well and doped barriers. The consistent
analysis shows that in the structures where electrons occupy the states in
quantum well only, all the temperature and magnetic field dependencies of the
components of resistivity tensor are well described by the theories of quantum
corrections. The contribution of electron-electron interaction to the
conductivity have been determined reliably in the structures with different
electron density. A possible reason of large scatter in experimental data
concerning the contribution of electron-electron interaction, obtained in
previous papers, and the role of the carriers, occupied the states of the doped
layers, is discussed.Comment: 10 pages with 9 figure
Spin Transistor and Quantum Spin Hall Effects in CdBxF2-x - p-CdF2 - CdBxF2-x Sandwich Nanostructures
Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the
surface of the n-type CdF2 bulk crystal are studied to register the spin
transistor and quantum spin Hall effects. The current-voltage characteristics
of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the
quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by
the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of
the resistance, specific heat and magnetic susceptibility demonstrate the high
temperature superconductor properties for the CdBxF2-x delta-barriers. The
value of the superconductor energy gap, 102.06 meV, determined by the tunneling
spectroscopy method appears to be in a good agreement with the relationship
between the zero-resistance supercurrent in superconductor state and the
conductance in normal state at the energies of the 2D hole subbands. The
results obtained are evidence of the important role of the multiple Andreev
reflections in the creation of the high spin polarization of the 2D holes in
the edged channels of the sandwich device. The high spin hole polarization in
the edged channels is shown to identify the mechanism of the spin transistor
and quantum spin Hall effects induced by varying the top gate voltage, which is
revealed by the first observation of the Hall quantum conductance staircase.Comment: 5 pages, 9 figure
Abelian-Projected Effective Gauge Theory of QCD with Asymptotic Freedom and Quark Confinement
We give an outline of a recent proof that the low-energy effective gauge
theory exhibiting quark confinement due to magnetic monopole condensation can
be derived from QCD without any specific assumption. We emphasize that the
low-energy effective abelian gauge theories obtained here give the dual
description of the same physics in the low-energy region. They show that the
QCD vacuum is nothing but the dual (type II) superconductor.Comment: 15 pages, Latex, no figures, Talk given at YKIS'97, Non-perturbative
QCD, Kyot
Abelian-Projected Effective Gauge Theory of QCD with Asymptotic Freedom and Quark Confinement
Starting from SU(2) Yang-Mills theory in 3+1 dimensions, we prove that the
abelian-projected effective gauge theories are written in terms of the maximal
abelian gauge field and the dual abelian gauge field interacting with monopole
current. This is performed by integrating out all the remaining non-Abelian
gauge field belonging to SU(2)/U(1). We show that the resulting abelian gauge
theory recovers exactly the same one-loop beta function as the original
Yang-Mills theory. Moreover, the dual abelian gauge field becomes massive if
the monopole condensation occurs. This result supports the dual superconductor
scenario for quark confinement in QCD. We give a criterion of dual
superconductivity and point out that the monopole condensation can be estimated
from the classical instanton configuration. Therefore there can exist the
effective abelian gauge theory which shows both asymptotic freedom and quark
confinement based on the dual Meissner mechanism. Inclusion of arbitrary number
of fermion flavors is straightforward in this approach. Some implications to
lower dimensional case will also be discussed.Comment: 39 pages, Latex, no figures, (2.2, 4.1, 4.3 are modified; 4.4,
Appendices A,B,C and references are added. No change in conclusion
Relaxation Effects in the Transition Temperature of Superconducting HgBa2CuO4+delta
In previous studies on a number of under- and overdoped high temperature
superconductors, including YBa_{2}Cu_{3}O_{7-y} and Tl_{2}Ba_{2}CuO_{6+\delta},
the transition temperature T_c has been found to change with time in a manner
which depends on the sample's detailed temperature and pressure history. This
relaxation behavior in T_c is believed to originate from rearrangements within
the oxygen sublattice. In the present high-pressure studies on
HgBa_{2}CuO_{4+\delta} to 0.8 GPa we find clear evidence for weak relaxation
effects in strongly under- and overdoped samples () with
an activation energy . For overdoped
HgBa_{2}CuO_{4+\delta} E_{A} increases under pressure more rapidly than
previously observed for YBa_{2}Cu_{3}O_{6.41}, yielding an activation volume of
+11 \pm 5 cm^{3}; the dependence of T_c on pressure is markedly nonlinear, an
anomalous result for high-T_c superconductors in the present pressure range,
giving evidence for a change in the electronic and/or structural properties
near 0.4 GPa
Development of a rapid inviscid-boundary layer aerodynamics tool
Hypersonic vehicles, combined with scramjet propulsion, offer significant and unique flexibility, performance and reusability benefits over rockets. These characteristics will likely reduce the cost of access-to-space. However, the realisation of such vehicles is significantly complicated by engine performance requirements which dictate relatively low altitude, high dynamic pressure trajectories. The thick atmosphere and high velocities result in high aerodynamic drag and heating. This paper introduces a simple, aerothermodynamic model for the analysis of hypersonic vehicles using Cart3D to calculate the inviscid flow-field and provide edge conditions to boundary layer calculations. Comparisons are made between two viscous methods of varying fidelity; flat plate correlations for skin friction with a simplified running length calculation and integral methods applied along inviscid, surface streamlines. Three validation cases are presented; (1) a hypersonic, blunt body; (2) a delta-wing, lifting body at subsonic to hypersonic Mach numbers and (3) a hypersonic, realistic vehicle configuration with internal flow-paths. In general, Cart3D predicts the lift and pitching moment coefficients well but consistently under-predicts drag given the absence of shear stress. The viscous contribution to aerodynamic forces was found to be adequately modelled using flat plate correlations and a simple Euclidean distance in place of the true running length. Preliminary results, however, suggest predictions of surface heat transfer rates benefit from a streamline running length and higher fidelity boundary layer methods
Optical properties of gyrotropic crystals in an ultrasound field. II. Natural polarizations and eigenvalues
Magnetic and EPR studies of the EuFe 3(BO 3) 4 single crystal
Magnetic and electron paramagnetic resonance (EPR) properties of
EuFe3(BO3)4 single crystals have been studied over the
temperature range of 300–4.2 K and in a magnetic field up to 5 T. The
temperature, field and orientation dependences of susceptibility,
magnetization and EPR spectra are presented. An antiferromagnetic ordering
of the Fe subsystem occurs at about 37 K. The easy direction of
magnetization perpendicular to the c axis is determined by magnetic
measurements. Below 10 K, we observe an increase of susceptibility connected
with the polarization of the Eu sublattice by an effective exchange field of
the ordered Fe magnetic subsystem. In a magnetic field perpendicular to the
c axis, we have observed an increase of magnetization at T < 10 K in the
applied magnetic field, which can be attributed to the appearance of the
magnetic moment induced by the magnetic field applied in the basal plane.
According to EPR measurements, the distance between the maximum and minimum
of derivative of absorption line of the Lorentz type is equal to 319 Gs. The
anisotropy of g-factor and linewidth is due to the influence of crystalline
field of trigonal symmetry. The peculiarities of temperature dependence of
both intensity and linewidth are caused by the influence of excited states
of europium ion (Eu3+). It is supposed that the difference between the
g-factors from EPR and the magnetic measurements is caused by exchange
interaction between rare earth and Fe subsystems via anomalous Zeeman
effect