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Microscopic Theory (microscopic + theory)

Distribution by Scientific Domains

Physics and Astronomy	60%
Chemistry	40%

Selected Abstracts

Microscopic theory for intersubband spontaneous emission

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2007
M. F. Pereira Jr.
Abstract The amplified spontaneous emission spectra of quantum-cascade laser structures is computed with a Keldysh Green's functions theory. We show that the emission spectra are sharpened in comparison to gain spectra due to wave guide propagation. In addition the different dependence on level occupation causes moderate differences between gain and emission peak positions. Our fit-parameter-free theory is valid in ranges of strong nonequilibrium, where fit-parameters do not even exist. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Pressure Dependence of Exchange Parameters and Neel Temperature in La2CuO4

ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2007
Anatolii Ya.
Microscopic mechanisms responsible for the observed pressure dependencies of the Neel temperature TN and parameters of isotropic and anisotropic exchange interaction in the orthorhombic antiferromagnet La2CuO4 are investigated. Within the framework of the Anderson microscopic theory of superexchange interaction, the expressions establishing interrelation between parameters of isotropic and anisotropic (both symmetric and antisymmetric) exchange interactions and by the structural parameters describing the Cu-O-Cu bonding angle and the Cu-O bond length in La2CuO4 are obtained. Experimentally determined pressure dependencies of structural parameters by H. Takahashi et al., allow one to present pressure dependencies of exchange parameters and TN in an apparent form. [source]

Exciton-spin relaxation in weakly confining quantum dots due to spin,orbit interaction

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006
E. Tsitsishvili
Abstract In weakly confining quantum structures such as interfacial islands or quantum disks the exciton-spin relaxation is governed by two independent electron and hole spin flip processes between the optically active and dark states. A microscopic theory for these transitions is presented which is based on second order spin,orbit and carrier,phonon interaction processes. We found that the sequential relaxation between bright and dark states leads to much faster exciton-spin relaxation than for strongly confining ("small") quantum dots where the dominant process stems from electron,hole exchange interaction plus hole deformation potential coupling. In addition, the fast exciton spin relaxation implies that the (exciton-bound) electron spin flip time is also much shorter than for a single electron. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ginzburg,Landau equations and boundary conditions for superconductors in static magnetic fields

ANNALEN DER PHYSIK, Issue 5 2005
J. Bünemann
Abstract We derive the Ginzburg,Landau equations for superconductors in static magnetic fields. Instead of the square of the gauge-invariant gradient of the order-parameter wave function, we consider the quantum-mechanical expression for the kinetic energy in the Ginzburg,Landau energy functional. We introduce a new surface term in the free energy functional which results in the de Gennes interface conditions. The phenomenological Ginzburg,Landau theory thus contains three length scales which must be determined from microscopic theory: the Ginzburg,Landau coherence length, the London penetration depth, and the de Gennes length. [source]

Meniscus deformation and dynamics of moving contact line between poly(ethylene terephthalate) surface and glycerol,water mixtures

ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 2 2009
Dr Stoyan I. Karakashev
Abstract The microscopic hydrodynamic (HD) and macroscopic theories for describing the meniscus deformation and dynamics of a moving contact line have been analyzed and compared by using the extrapolated dynamic contact angles between a poly(ethylene terephthalate) (PET) surface and glycerol,water mixtures. The analysis showed that the microscopic theory is confined by the microscopic length scale and small capillary number. The macroscopic theory is not subjected to any restrictions. Three (inner, intermediate and outer) regions of the dynamic meniscus have been combined by using the contact molecular kinetics and hydrodynamics. The combined molecular-HD theory has been validated using the experimental data for the extrapolated dynamic contact angles between a PET surface and glycerol,water mixtures. The analysis showed that the combined theory describes the phenomenon of wetting qualitatively. It was found that the contradiction within the theoretical framework of the molecular kinetics and hydrodynamics hinders the exact description of the wetting phenomenon. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source]