53 research outputs found
Hall helps Ohm: some corrections to negative-U centers approach to transport properties of YBaCuO and LaSrCuO
For broad oxygen and strontium doping ranges, temperature dependences
(T-dependences) of the normal state resistivity \rho(T) of YBa_2Cu_3O_x (YBCO)
and La_(2-x)Sr_xCuO_4 (LSCO) are calculated and compared to experiments. Holes
transport was taken in the \tau-approximation, where \tau(T,\epsilon) is due to
acoustic phonons. Besides, T-dependence of the chemical potential \mu(T) and
effective carrier mass m* ~10-100 free electron masses, obtained by negative-U
centers modelling the T-dependence of the Hall coefficient, were used to
calculate \rho(T). In addition, it is demonstrated that anisotropy of the
cuprates does not affect the calculated T-variation of neither Hall coefficient
nor \rho, but only rescale their magnitudes by factors depending on
combinations of m_ab and m_c.Comment: 4th International Conference Fundamental Problems of High-Temperature
Superconductivity, Moscow-Zvenigorod (October 3-7, 2011) Submitted to J.
Supercond. Nov. Magn.: after revision. Extension for Supercond. Sci. Technol.
24 075026 (2011), DOI: 10.1088/0953-2048/24/7/075026 Contains: 2 pages, 3
figure
Electron density stratification in two-dimensional structures tuned by electric field
A new kinetic instability which results in formation of charge density waves
is proposed. The instability is of a purely classical nature. A spatial period
of arising space-charge and field configuration is inversely proportional to
electric field and can be tuned by applied voltage. The instability has no
interpretation in the framework of traditional hydrodynamic approach, since it
arises from modulation of an electron distribution function both in coordinate
and energy spaces. The phenomenon can be observed in thin 2D nanostructures at
relatively low electron density.Comment: 4 pages, 2 figure
Radio-frequency discharges in Oxygen. Part 1: Modeling
In this series of three papers we present results from a combined
experimental and theoretical effort to quantitatively describe capacitively
coupled radio-frequency discharges in oxygen. The particle-in-cell Monte-Carlo
model on which the theoretical description is based will be described in the
present paper. It treats space charge fields and transport processes on an
equal footing with the most important plasma-chemical reactions. For given
external voltage and pressure, the model determines the electric potential
within the discharge and the distribution functions for electrons, negatively
charged atomic oxygen, and positively charged molecular oxygen. Previously used
scattering and reaction cross section data are critically assessed and in some
cases modified. To validate our model, we compare the densities in the bulk of
the discharge with experimental data and find good agreement, indicating that
essential aspects of an oxygen discharge are captured.Comment: 11 pages, 10 figure
Collisionless heating in radio-frequency discharges: a review
Radio-frequency discharges are practically and scientifically interesting. A practical understanding of such discharges requires, among other things, a quantitative appreciation of the mechanisms involved in heating electrons, since this heating is the proximate
cause of the ionization that sustains the plasma. When these discharges are operated at sufficiently low pressure, collisionless electron heating can be an important and even the dominant mechanism. Since the low pressure regime is important for many applications, understanding collisionless heating is both theoretically and
practically important. This review is concerned with the state of theoretical knowledge of collisionless heating in both inductive and capacitive discharges
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