767 research outputs found
Room temperature coherent spin alignment of silicon vacancies in 4H- and 6H-SiC
We report the realization of the optically induced inverse population of the
ground-state spin sublevels of the silicon vacancies () in
silicon carbide (SiC) at room temperature. The data show that the probed
silicon vacancy spin ensemble can be prepared in a coherent superposition of
the spin states. Rabi nutations persist for more than 80 s. Two opposite
schemes of the optical alignment of the populations between the ground-state
spin sublevels of the silicon vacancy upon illumination with unpolarized light
are realized in 4H- and 6H-SiC at room temperature. These altogether make the
silicon vacancy in SiC a very favorable defect for spintronics, quantum
information processing, and magnetometry.Comment: 4 pages, 3 picture
The multiplicity and the spectra of secondaries correlated with the leading particle energy
The spectra of leading particles of different nature in pp-collisions at E sub 0 = 33 GeV are obtained. The multiplicities and the spectra of secondaries, mesons, gamma-quanta, lambda and lambda-hyperons and protons for different leading particle energy ranges are determined
Математические начала ранней Вселенной и живой материи
We suppose that our Universe sprang according to the Cayley algebra. The Great Nothing is described by this algebra (no having any representation). But it may be enclosed into the Heisenberg algebra (the enclosing is not homomorphism). A new physical substance, called pre-matter (or bi-Hamiltonian matter), is underlain the latter. Our Universe has consisted of this kind of matter in its zero cycle. After the Big Bang that is identified with the total irreversible quantum transition, taking place in the bi-Hamiltonian matter, the fundamental particles were arisen. It is shown that after the so called de Sitter’s stage of Universe extension our space was in phase of the Bohr compact (space firm). Formation of alive cells were connected with this phase state of our space.Было ли у Вселенной начало, которое можно принять за акт творения, или она как causa sui существует сама по себе вечно и бесконечно? Этот вопрос, весьма актуальный в современной космологии, до сих пор не имел однозначного ответа. В данной статье начало Вселенной (Великое Ничто) отождествляется с алгеброй Кэли. Исходя из нее, дается последовательное построение физической картины мира, которая включает в себя: 1) материализацию Ничто — возникновение праматерии , 2) появление конфигурационного пространства — носителя праматерии, способного находиться в трех различных фазовых состояниях, 3) возникновение наблюдаемой материи вследствие конденсации и взрыва праматерии — тотального квантового перехода, происходящего в праматерии, и, в частности, образование живой клетки, которое происходит в той фазе пространства, которая называется боровским компактом. Важную роль играют квантовые корреляции, определяющие топологию конфигурационного пространства праматерии
Admittance spectroscopy of CdTe/CdS solar cells subjected to varied nitric-phosphoric etching conditions
In this work we investigate the electric and structural properties of CdTe/CdS solar cells subjected to a nitric-phosphoric (NP) acid etching procedure, employed for the formation of a Te-rich layer before back contacting. The etching time is used as the only variable parameter in the study, while admittance spectroscopy is employed for the characterization of the cells' electric properties as well as for the analysis of the defect energy levels. Particular attention was also given to the characteristics of unetched devices and it is shown that despite the larger height of back-contact barrier such samples show well defined admittance spectra, as well as allow for extraction of as much as five defect levels in the range of 0.08-0.9 eV above the valence band. In contrast, admittance characteristics of the etched samples show a decrease of the number of the detectable trap levels with increasing etching time. (Hence it is usual for only one or two trap levels to be reported in the literature for finished devices.) The latter leads to the anomalous Arrhenius energy plots as well as the breakdown of low-frequency capacitance characteristics for samples etched with times larger than 30 s. The observed effects are attributed to physical thinning of the cells, the etching out of grain boundaries, and the tellurium enrichment of the CdTe surface by NP etching. We also perform analysis of the back-contact barrier height as extracted from dark I-V measurements at different temperatures. The dependence of this barrier height on NP etching time is compared with that of conversion efficiency, from which conclusions are drawn about both positive and negative effects of the nitric-phosphoric etch
Interactions in high-mobility 2D electron and hole systems
Electron-electron interactions mediated by impurities are studied in several
high-mobility two-dimensional (electron and hole) systems where the parameter
changes from 0.1 to 10 ( is the momentum relaxation
time). This range corresponds to the \textit{intermediate} and \textit
{ballistic} regimes where only a few impurities are involved in
electron-electron interactions. The interaction correction to the Drude
conductivity is detected in the temperature dependence of the resistance and in
the magnetoresistance in parallel and perpendicular magnetic fields. The
effects are analysed in terms of the recent theories of electron interactions
developed for the ballistic regime. It is shown that the character of the
fluctuation potential (short-range or long-range) is an important factor in the
manifestation of electron-electron interactions in high-mobility 2D systems.Comment: 22 pages, 11 figures; to appear in proceedings of conference
"Fundamental Problems of Mesoscopic Physics", Granada, Spain, 6-11 September,
200
On the Electron-Electron Interactions in Two Dimensions
In this paper, we analyze several experiments that address the effects of
electron-electron interactions in 2D electron (hole) systems in the regime of
low carrier density. The interaction effects result in renormalization of the
effective spin susceptibility, effective mass, and g*-factor. We found a good
agreement among the data obtained for different 2D electron systems by several
experimental teams using different measuring techniques. We conclude that the
renormalization is not strongly affected by the material or sample-dependent
parameters such as the potential well width, disorder (the carrier mobility),
and the bare (band) mass. We demonstrate that the apparent disagreement between
the reported results on various 2D electron systems originates mainly from
different interpretations of similar "raw" data. Several important issues
should be taken into account in the data processing, among them the dependences
of the effective mass and spin susceptibility on the in-plane field, and the
temperature dependence of the Dingle temperature. The remaining disagreement
between the data for various 2D electron systems, on one hand, and the 2D hole
system in GaAs, on the other hand, may indicate more complex character of
electron-electron interactions in the latter system.Comment: Added refs; corrected typos. 19 pages, 7 figures. To be published in:
Chapter 19, Proceedings of the EURESCO conference "Fundamental Problems of
Mesoscopic Physics ", Granada, 200
In-plane Magnetoconductivity of Si-MOSFET's: A Quantitative Comparison between Theory and Experiment
For densities above cm in the strongly
interacting system of electrons in two-dimensional silicon inversion layers,
excellent agreement between experiment and the theory of Zala, Narozhny and
Aleiner is obtained for the response of the conductivity to a magnetic field
applied parallel to the plane of the electrons. However, the Fermi liquid
parameter and the valley splitting obtained from
fits to the magnetoconductivity, although providing qualitatively correct
behavior (including sign), do not yield quantitative agreement with the
temperature dependence of the conductivity in zero magnetic field. Our results
suggest the existence of additional scattering processes not included in the
theory in its present form
The so-called two dimensional metal-insulator transition
We provide a critical perspective on the collection of low-temperature
transport phenomena in low-density two-dimensional semiconductor systems often
referred to as the 2D metal-insulator transition. We discuss the physical
mechanisms underlying the anomalous behavior of the two-dimensional effective
metallic phase and the metal-insulator transition itself. We argue that a key
feature of the 2D MIT physics is the long-range bare Coulombic disorder arising
from the random distribution of charged impurities in the low-density 2D
semiconductor structures.Comment: 12 pages, 4 figures; Revised final version with additional references
and some modifications in the tex
Effects of Electron-Electron and Electron-Phonon Interactions in Weakly Disordered Conductors and Heterostuctures
We investigate quantum corrections to the conductivity due to the
interference of electron-electron (electron-phonon) scattering and elastic
electron scattering in weakly disordered conductors. The electron-electron
interaction results in a negative -correction in a 3D conductor. In
a quasi-two-dimensional conductor, ( is the thickness, is
the Fermi velocity), with 3D electron spectrum this correction is linear in
temperature and differs from that for 2D electrons (G. Zala et. al., Phys.
Rev.B {\bf 64}, 214204 (2001)) by a numerical factor. In a
quasi-one-dimensional conductor, temperature-dependent correction is
proportional to . The electron interaction via exchange of virtual phonons
also gives -correction. The contribution of thermal phonons interacting
with electrons via the screened deformation potential results in -term and
via unscreened deformation potential results in -term. The interference
contributions dominate over pure electron-phonon scattering in a wide
temperature range, which extends with increasing disorder.Comment: 6 pages, 2figure
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