81 research outputs found
Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules
We investigate anharmonically coupled high- and low-frequency excitations in
a planar lattice of adsorbed molecules interacting with phonons of a crystal.
Dephasing of high-frequency local vibrations by low-frequency resonance modes
is described in terms of temperature Green's function. The equations obtained
are solved, first, with a small ratio of the anharmonic coupling coefficient
for high- and low-frequency modes to the resonance width, and second, in the
low-temperature limit. High-frequency spectral line positions and widths depend
on dispersion laws and resonance mode lifetimes. It is shown that lateral
interactions of low-frequency modes of adsorbed molecules can lead to a
significant narrowing of high-frequency spectral lines, which is consistent
with experimental data.Comment: REVTeX, 11 pages, no figure
Hydrogen atom moving across a strong magnetic field: analytical approximations
Analytical approximations are constructed for binding energies,
quantum-mechanical sizes and oscillator strengths of main radiative transitions
of hydrogen atoms arbitrarily moving in magnetic fields 10^{12}-10^{13} G.
Examples of using the obtained approximations for determination of maximum
transverse velocity of an atom and for evaluation of absorption spectra in
magnetic neutron star atmospheres are presented.Comment: 17 pages, 3 figures, 5 tables, LaTeX with IOP style files (included).
In v.2, Fig.1 and Table 5 have been corrected. In v.3, a misprint in the fit
for oscillator strengths, Eq.(21), has been correcte
Inelastic Light Scattering From Correlated Electrons
Inelastic light scattering is an intensively used tool in the study of
electronic properties of solids. Triggered by the discovery of high temperature
superconductivity in the cuprates and by new developments in instrumentation,
light scattering both in the visible (Raman effect) and the X-ray part of the
electromagnetic spectrum has become a method complementary to optical
(infrared) spectroscopy while providing additional and relevant information.
The main purpose of the review is to position Raman scattering with regard to
single-particle methods like angle-resolved photoemission spectroscopy (ARPES),
and other transport and thermodynamic measurements in correlated materials.
Particular focus will be placed on photon polarizations and the role of
symmetry to elucidate the dynamics of electrons in different regions of the
Brillouin zone. This advantage over conventional transport (usually measuring
averaged properties) indeed provides new insights into anisotropic and complex
many-body behavior of electrons in various systems. We review recent
developments in the theory of electronic Raman scattering in correlated systems
and experimental results in paradigmatic materials such as the A15
superconductors, magnetic and paramagnetic insulators, compounds with competing
orders, as well as the cuprates with high superconducting transition
temperatures. We present an overview of the manifestations of complexity in the
Raman response due to the impact of correlations and developing competing
orders. In a variety of materials we discuss which observations may be
understood and summarize important open questions that pave the way to a
detailed understanding of correlated electron systems.Comment: 62 pages, 48 figures, to appear in Rev. Mod. Phys. High-resolution
pdf file available at http://onceler.uwaterloo.ca/~tpd/RMP.pd
Effects of anharmonic strain on phase stability of epitaxial films and superlattices: applications to noble metals
Epitaxial strain energies of epitaxial films and bulk superlattices are
studied via first-principles total energy calculations using the local-density
approximation. Anharmonic effects due to large lattice mismatch, beyond the
reach of the harmonic elasticity theory, are found to be very important in
Cu/Au (lattice mismatch 12%), Cu/Ag (12%) and Ni/Au (15%). We find that
is the elastically soft direction for biaxial expansion of Cu and Ni, but it is
for large biaxial compression of Cu, Ag, and Au. The stability of
superlattices is discussed in terms of the coherency strain and interfacial
energies. We find that in phase-separating systems such as Cu-Ag the
superlattice formation energies decrease with superlattice period, and the
interfacial energy is positive. Superlattices are formed easiest on (001) and
hardest on (111) substrates. For ordering systems, such as Cu-Au and Ag-Au, the
formation energy of superlattices increases with period, and interfacial
energies are negative. These superlattices are formed easiest on (001) or (110)
and hardest on (111) substrates. For Ni-Au we find a hybrid behavior:
superlattices along and like in phase-separating systems, while for
they behave like in ordering systems. Finally, recent experimental
results on epitaxial stabilization of disordered Ni-Au and Cu-Ag alloys,
immiscible in the bulk form, are explained in terms of destabilization of the
phase separated state due to lattice mismatch between the substrate and
constituents.Comment: RevTeX galley format, 16 pages, includes 9 EPS figures, to appear in
Physical Review
Use of electronic educational technologies for distance training to mathematical disciplines
The paper describes developed at the Department of mathematics St. Petersburg state marine technical University software products for that implement the elements of distance education in the educational process. These include: virtual textbooks and system of testing. When developing virtual textbooks used modular principle, and as a virtual learning environment is implemented on the Sakai platform.В работе описываются разработанные на кафедре математики Санкт-Петербургского государственного морского технического университета программные продукты, позволяющие реализовать элементы дистанционного образования в учебном процессе. К ним относятся: виртуальные учебники и система тестирования. При разработке виртуальных учебников использовался модульный принцип, а в качестве виртуальная образовательная среда реализована на платформе Saka
Superconductivity in Silicon Nanostructures
We present the findings of the superconductivity in the silicon
nanostructures prepared by short time diffusion of boron after preliminary
oxidation of the n-type Si (100) surface. These Si-based nanostructures
represent the p-type high mobility silicon quantum well (Si-QW) confined by the
delta - barriers heavily doped with boron. The ESR studies show that the delta
- barriers appear to consist of the trigonal dipole centers, B(+)-B(-), which
are caused by the negative-U reconstruction of the shallow boron acceptors,
2B(0)=>B(+)-B(-). The temperature and magnetic field dependencies of the
resistance, thermo-emf, specific heat and magnetic susceptibility demonstrate
that the high temperature superconductivity observed seems to result from the
transfer of the small hole bipolarons through these negative-U dipole centers
of boron at the Si-QW - delta - barrier interfaces. The value of the
superconductor energy gap obtained is in a good agreement with the data derived
from the oscillations of the conductance in normal state and of the
zero-resistance supercurrent in superconductor state as a function of the bias
voltage. These oscillations appear to be correlated by on- and off-resonance
tuning the two-dimensional subbands of holes with the Fermi energy in the
superconductor delta - barriers. Finally, the proximity effect in the S- Si-QW
-S structure is revealed by the findings of the multiple Andreev reflection
(MAR) processes and the quantization of the supercurrent
Multi-phonon transitions in II-VI quantum dot
The intensity of polaron exciton absorption in a spherical
quantum dot is calculated. The localized electrons and holes are
shown to interact with long-wavelength phonons with wave vectors
, R being the radius of the dot.
In the case of strong electron-phonon interaction,
the polaron effect results in multiple phonon replicas of exciton optical
transition. The broadening of
different phonon replicas is shown to be less than their separation
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