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 $q \approx 1/R$, 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