Proton-induced L x-ray spectra of heavy elements have been recorded with a Si(Li) x-ray spectrometer of accurately determined resolution function. The intrinsic widths of the Ll and Lα1 lines were obtained by a nonli...
Proton-induced L x-ray spectra of heavy elements have been recorded with a Si(Li) x-ray spectrometer of accurately determined resolution function. The intrinsic widths of the Ll and Lα1 lines were obtained by a nonlinear-least squares fitting procedure. Lα1 widths agree with relativistic independent-particle-model (IPM) calculations, but Ll widths fall some 10–30 % below predictions. This indicates a strong influence of many-body effects on the decay of the 3s hole state; a similar influence is already well established for the 2s state. Relative intensities of the weak, electric-dipole-forbidden lines Lt and Ls are in good accord with IPM calculations.
The doping and the temperature dependence of various normal-state properties of high-temperature superconductors are studied by applying the t-t’-J model. The slave-boson method is used to treat the strong correlatio...
The doping and the temperature dependence of various normal-state properties of high-temperature superconductors are studied by applying the t-t’-J model. The slave-boson method is used to treat the strong correlations. The fermion quasiparticles carry both charge and spin and the volume of the Fermi surface satisfies the Luttinger theorem. The quasiparticle energy spectrum used in the calculation is obtained from a mean-field treatment of the t-t’-J model. The study is confined to the metallic phase where contributions from the t and t’ terms are most dominant. The calculations provide a quantitative understanding for the doping dependence of Drude plasma frequency, Hall resistivity RH, band Pauli magnetic susceptibility χSB, thermopower, and the room-temperature dc conductivity. The temperature dependence of RH and χSB for small doping are not understood. The calculated density of states, Fermi energy, effective mass, and the Sommerfeld parameter have reasonable values. We have taken J=0 and t=0.45 eV and have considered a wide range of t’ values.
A path-integral formulation of the two-dimensional Hubbard model is used in which scattering of electrons across the magnetic Brillouin zone by spin fluctuations (umklapp processes) is included. With this formulation,...
A path-integral formulation of the two-dimensional Hubbard model is used in which scattering of electrons across the magnetic Brillouin zone by spin fluctuations (umklapp processes) is included. With this formulation, we have calculated the spin-wave velocity cs and the specific heat Cv for the half-filled-band case. For the quadratic form of the Hubbard model due to Schrieffer, we obtain cs=1.5c0 in the large-U limit (U is the intrasite Coulomb repulsion, c0= √2 J is the spin-wave velocity in linear-spin-wave theory, J=4t2/U is the superexchange interaction, and t is the hopping integral for nearest neighbors). Our result is in good agreement with various numerical calculations based on the Heisenberg model, e.g., cs=1.22c0 by Liu and Manousakis [Phys. Rev. B 40, 11 437 (1989)], with use of the variational Monte Carlo technique. Our present calculation differs from previous path-integral calculations, which lead to cs∼t in the large-U limit. A general free-energy formula, which includes all kinds of fluctuation, is obtained. At low temperature, the specific heat in the large-U limit is given by Cv≃0.51(T/J)2. The present calculation can also be applied to the Hubbard model written in other quadratic forms, in one of which the saddle-point approximation leads to the Hartree-Fock solution and cs=c0 and Cv=1.15(T/J)2 in the large-U limit.
A general analysis of the two-body Dirac equation is presented for the case of equal masses interacting via a static Coulomb potential. Radial equations are derived and their analytical structure is discussed. Standar...
A general analysis of the two-body Dirac equation is presented for the case of equal masses interacting via a static Coulomb potential. Radial equations are derived and their analytical structure is discussed. Standard analytical and perturbative methods have failed to provide solutions to the radial equations due to the presence of the singularity on the negative radial axis at roughly the distance of the classical electron radius. The exact radial equations are solved using finite-element analysis, and the low-lying bound states are obtained to an accuracy of one part in 1018. The effect of the singularity is clearly seen in the structure of the finite-element radial components.
A relativistic gravitational theory in (1 + 1) dimensions is presented which exhibits many of the qualitative features of (3 + 1)-dimensional general relativity. The field equations are simple enough for undergraduate...
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A relativistic gravitational theory in (1 + 1) dimensions is presented which exhibits many of the qualitative features of (3 + 1)-dimensional general relativity. The field equations are simple enough for undergraduates to solve yet rich enough in structure to form a useful pedagogical example for exploring the qualitative features of relativistic gravitation. Black hole solutions to the field equations of the theory are derived and its relationship to Newtonian gravity is discussed in detail.
A new confocal scanning-stage transmitted-light and reflected-light laser microscope is described. In addition to allowing confocal transmitted-light imaging, this microscope has the unique feature of imaging both the...
A new confocal scanning-stage transmitted-light and reflected-light laser microscope is described. In addition to allowing confocal transmitted-light imaging, this microscope has the unique feature of imaging both the top and bottom of a specimen in reflected light, with the two images in perfect registration. Only one detector is used;different imaging modes can be selected by simple rotation of the polarizers. Several confocal images are presented, chosen to illustrate the unique features of the instrument.
Accurate tail-to-peak intensity ratios are extracted from the spectra produced in a Si(Li) detector by x-rays of energies 2-10 keV. The widely used model of a surface layer of incomplete charge collection fails to exp...
Accurate tail-to-peak intensity ratios are extracted from the spectra produced in a Si(Li) detector by x-rays of energies 2-10 keV. The widely used model of a surface layer of incomplete charge collection fails to explain the energy dependence of these data. The model is augmented to include loss of photoelectrons travelling back into the ICC layer from an interaction in the active silicon region;this gives excellent agreement with experiment. It is shown that the detection efficiency in the region of low x-ray energy may be deduced from the tail-to-peak ratios, together with measurement of the thicknesses of the beryllium window and the metal contact;a potential source of error in measuring the latter by the popular fluorescence technique is demonstrated.
First-principles theoretical results are reported for the specific heats and closely related thermodynamic quantities, required in the determination of the characteristics of the supercooled metallic liquids, for Al, ...
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First-principles theoretical results are reported for the specific heats and closely related thermodynamic quantities, required in the determination of the characteristics of the supercooled metallic liquids, for Al, Rb and Ca0.7Mg0.3 metals. Of these results, those for the specific heats are fully analyzed and discussed by considering computer-simulation results on the atomic motion in the supercooled-liquid region. It now appears that the specific heat at constant pressure behaves as a monotonically increasing function of temperature in decreasing from the melting temperature to the glass-transition temperature for those supercooled metallic liquids that have high glass-forming ability.
A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained re...
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A first-principles thermodynamic calculation appropriate for metallic glasses is first proposed and is then carried out for the metals Al and Ca0.7Mg0.3. The calculated results are compared with previously obtained results for the supercooled-liquid states of pure Al metal. It now appears that, because of the significant change in the derivative of the volume with respect to temperature on going through the liquid-glass transition, the thermodynamic quantities vary drastically in this region, for those metals that can form glasses in the laboratory through the liquid-quenching process.
The dc-conductivity, plasma frequency and the specific heat are calculated as a function of doping for La2-xSrxCuO4 and related compounds. There is good quantitative agreement with experimental data. The volume includ...
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The dc-conductivity, plasma frequency and the specific heat are calculated as a function of doping for La2-xSrxCuO4 and related compounds. There is good quantitative agreement with experimental data. The volume included by the Fermi surface obeys Luttinger Theorem. The calculations are based on quasiparticles whose energy spectrum has tight binding form renormalized by strong correlations and originating from the t-t'-J model. We have used the relaxation time approximation.
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