188 research outputs found
Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4
We performed far-infrared and submillimeter-wave conductivity experiments in
the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime,
T_c = 25 K). The onset of the absorption in the superconducting state is
gradual in frequency and is inconsistent with the isotropic s-wave gap.
Instead, a narrow quasiparticle peak is observed at zero frequency and a second
peak at finite frequencies, clear fingerprints of the conductivity in a d-wave
superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0,
or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the
spin-fluctuations. The infrared conductivity as well as the suppression of the
quasiparticle scattering rate below T_c are qualitatively similar to the
results in the hole-doped cuprates.Comment: 5 pages, 4 figures include
The R.I. Pimenov unified gravitation and electromagnetism field theory as semi-Riemannian geometry
More then forty years ago R.I. Pimenov introduced a new geometry --
semi-Riemannian one -- as a set of geometrical objects consistent with a
fibering He suggested the heuristic principle according to
which the physically different quantities (meter, second, coulomb etc.) are
geometrically modelled as space coordinates that are not superposed by
automorphisms. As there is only one type of coordinates in Riemannian geometry
and only three types of coordinates in pseudo-Riemannian one, a multiple
fibered semi-Riemannian geometry is the most appropriate one for the treatment
of more then three different physical quantities as unified geometrical field
theory.
Semi-Euclidean geometry with 1-dimensional fiber and
4-dimensional Minkowski space-time as a base is naturally interpreted as
classical electrodynamics. Semi-Riemannian geometry with the
general relativity pseudo-Riemannian space-time and 1-dimensional
fiber responsible for the electromagnetism, provides the unified field
theory of gravitation and electromagnetism. Unlike Kaluza-Klein theories, where
the 5-th coordinate appears in nondegenerate Riemannian or pseudo-Riemannian
geometry, the theory based on semi-Riemannian geometry is free from defects of
the former. In particular, scalar field does not arise.
PACS: 04.50.Cd, 02.40.-k, 11.10.KkComment: 16 pages, 2 figures. Submited to Physics of Atomic Nucle
Renewable resources as energy-efficient sources
This article provides the information about the concept of renewable resources as energy-efficient sources, its classification, methods of using, including the most innovative which are realized nowadays. The study offers a comprehensive description of all types of renewable energetic resources, exciting at this moment
Optical realization of magneto-intersubband oscillations
We report on the optical realization of the magneto-intersubband oscillations
that have been measured in the sub-terahertz transmittance of a GaAs quantum
well with two subbands occupied. Following their dc analogue, the oscillations
are periodic in the inverse magnetic field with the period governed by the
subband gap. Their magnitude and polarization dependence accurately follow the
presented simplified version of the dynamic magneto-intersubband oscillations
equation that naturally combines dc magneto-intersabband oscillations with
microwave-induced resistance oscillations (MIRO). Simultaneously measured
photoresistance also reveals its strong sensitivity to the sign of the circular
polarization, proving the used theoretical modeling.Comment: 5 pages, 2 figure
Four-loop verification of algorithm for Feynman diagrams summation in N=1 supersymmetric electrodynamics
A method of Feynman diagrams summation, based on using Schwinger-Dyson
equations and Ward identities, is verified by calculating some four-loop
diagrams in N=1 supersymmetric electrodynamics, regularized by higher
derivatives. In particular, for the considered diagrams correctness of an
additional identity for Green functions, which is not reduced to the gauge Ward
identity, is proved.Comment: 14 pages, 9 figure
Anisotropic conductivity of Nd_{1.85}Ce_{0.15}CuO_{4-\delta} films at submillimeter wavelengths
The anisotropic conductivity of thin NdCeCuO
films was measured in the frequency range 8 cm 40 cm and
for temperatures 4 K K. A tilted sample geometry allowed to extract
both, in-plane and c-axis properties. The in-plane quasiparticle scattering
rate remains unchanged as the sample becomes superconducting. The temperature
dependence of the in-plane conductivity is reasonably well described using the
Born limit for a d-wave superconductor. Below T_{{\rm C}%} the c-axis
dielectric constant changes sign at the screened c-axis plasma
frequency. The temperature dependence of the c-axis conductivity closely
follows the linear in T behavior within the plane.Comment: 4 pages, 4 figure
Polynomial reconstruction of electric charge distribution on the conductive plate caused by external electric field
The paper proposes an original method of calculating the charge distribution on the surface of the conductive plate introduced into the external electrostatic field. The authors managed to obtain the polynomials which allow to solve the integral equation that establishes the relationship between charge distribution of the conductive plate and the potential distribution of the external field and the potential on the surface of the plate. The proposed algorithms solutions are valid in the presence of axial symmetry of the field and the plate. Examples of calculation of conductor charge distribution in the presence of external field by using a polynomial expansion have been presented. The comparisons of results calculated by the polynomial method and by known analytical solutions have been given
Mechanical activation influence on the morphological properties of La[2]O[3]-TiO[2]-B
The influence of mechanical activation of the powder mixture used to obtain the high-perfomance cathode for accelerating engineering with the SHS-method has been explored. The mechanically processed mixtures have been morphologically analyzed. The optimal modes of mechanical activation have been determined for the mixture
Terahertz Conductivity at the Verwey Transition in Magnetite
The complex conductivity at the (Verwey) metal-insulator transition in
Fe_3O_4 has been investigated at THz and infrared frequencies. In the
insulating state, both the dynamic conductivity and the dielectric constant
reveal a power-law frequency dependence, the characteristic feature of hopping
conduction of localized charge carriers. The hopping process is limited to low
frequencies only, and a cutoff frequency nu_1 ~ 8 meV must be introduced for a
self-consistent description. On heating through the Verwey transition the
low-frequency dielectric constant abruptly decreases and becomes negative.
Together with the conductivity spectra this indicates a formation of a narrow
Drude-peak with a characteristic scattering rate of about 5 meV containing only
a small fraction of the available charge carriers. The spectra can be explained
assuming the transformation of the spectral weight from the hopping process to
the free-carrier conductivity. These results support an interpretation of
Verwey transition in magnetite as an insulator-semiconductor transition with
structure-induced changes in activation energy.Comment: 6 Pages, 3 Figure
High-field AFMR in single-crystalline La_{0.95}Sr_{0.05}MnO_3: Experimental evidence for the existence of a canted magnetic structure
High-field antiferromagnetic-resonance (AFMR) spectra were obtained in the
frequency range 60 GHz < \nu < 700 GHz and for magnetic fields up to 8 T in
twin-free single crystals of La_{0.95}Sr_{0.05}MnO_3. At low temperatures two
antiferromagnetic modes were detected, which reveal different excitation
conditions and magnetic field dependencies. No splitting of these modes was
observed for any orientation of the static magnetic field excluding the
phase-separation scenario for this composition. Instead, the full data set
including the anisotropic magnetization can be well described using a
two-sublattice model of a canted antiferromagnetic structure.Comment: 4 pages, 3 figure
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