Effect of Strong Electron-Phonon Interactions on an Interface Polaron

The present work deals with an electron interacting strongly with both bulk longitudinal optical (LO) phonons and interface (IF) optical phonons in which we adopt and generalize the Tokuda's variational method for studying the interface polaron properties in polar crystals at zero temperature, In our approach, we can reduce the Hamiltollian equation of the system to a pair of integro-differential equations in two variational parameters of the electron wavefunction from which we can calculate various physical properties of an interface polaron including the ground state energy, average numbers of interacting phonons, the average distance from the interface and the anisotropic effective masses of the interface polaron. Numerical results are obtained explicitly for LiF crystal interfaced with NaF crystal as well as other similar systems with varying physical constants, which show the typical trends of variations for the effects of strong electron-phonon interactions on different physical properties of an interface polaron.     

Influence of Electron-Phonon Interactions on the Physical Properties of an Interface Polaron

Taking into account the interactions of both bulk longitudinal optical (LO) pltonons and surface optical (SO) pltonons and using Haga's perturbatioit method, we derive an effective Hamiltonian for the interface magnetopolaron in polar crystals at zero temperature. We illustrate in details how to solve this effective Hamiltonian analytically and we obtain explicit formulae not on1y for the electron cyclotron mass associated with the Landau levels but also for the self-trapping energy of the magnetopolaron with respect to its first three quantum states in the direction normal to the interface of the system. Numerical results are calculated for some Ⅱ-Ⅵ and Ⅲ-Ⅴ semiconductor compounds,indicting that the bulk LO phonons and SO phonons do have different trends of effects on the electron in different quantum states.     

Experimental calibration and field investigation of the oxygen isotopic fractionation between biogenic aragonite and water

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.     

Effect of three-body forces on the lattice dynamics of noble metals

A simple method to generate an effective electron-ion interaction pseudopotential from the energy wave number characteristic obtained by first principles calculations has been suggested. This effective potential has been used, in third order perturbation, to study the effect of three-body forces on the lattice dynamics of noble metals. It is found that three-body forces, in these metals, do play an important role. The inclusion of such three-body forces appreciably improves the agreement between the experimental and theoretical phonon dispersion curves.     

Influence of the Parabolic Potential on the Interaction of Electron-Confined Phonons in a Quantum Wire

The Lee, Low and Pines' variational method is employed to study the interaction of electronconfined phonons within a rectangular quantum wire under an additional parabolic potential. Detailed mathematical derivation is carried out to obtain some formulire for the polaron selfenergy, the electron effective mass along the wire and the ground state energy; Using the idea of Fourier decomposition of wavefunctions, numerical calculations are performed for a typical GaAs quantum wire within the mesoscopic size. Our present results show that the effect of phonon confinement always reduces the magnitude of the electron-phonon interaction and the associated physical quwtities whereas the additional parabolic potential tends to enhance, both the electron-phonon interaction and the ground state energy. Comparing with previous calculations, our results also reveal the trends of those interesting physical quantities.