We have developed a spectrally resolved confocal microscope with high photon efficiency for photoluminescence and fluorescence measurements. A scanning grating is placed inside the detection arm of the microscope so t...
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If the lineshape response of a Si(Li) detector is measured using monoenergetic x-rays provided by a monochromator, it must be convoluted by a Lorentzian of appropriate width in order to represent the lineshape encount...
If the lineshape response of a Si(Li) detector is measured using monoenergetic x-rays provided by a monochromator, it must be convoluted by a Lorentzian of appropriate width in order to represent the lineshape encountered in directly measured x-ray spectra. It is shown that the Lorentzian component is responsible for a significant fraction of low-energy peak tailing, a phenomenon usually attributed to detector imperfections.
A new near infrared emission spectrum of (HeD)-He-4 has been recorded at 4.2 K during proton irradiation of a mixed sample of helium gas and solid deuterium. The upper state of the transitions is an admixture of the a...
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A new near infrared emission spectrum of (HeD)-He-4 has been recorded at 4.2 K during proton irradiation of a mixed sample of helium gas and solid deuterium. The upper state of the transitions is an admixture of the accidentally degenerate D(2)SIGMA+ (upsilon = 0) and C(2)SIGMA+ (upsilon = 3) levels. The lower state is the previously unobserved A(2)SIGMA+ (upsilon = 2) level. The observation of this levels allows for evaluation of the rotational constants B2" and D2" for the A(2)SIGMA+ state, and for a better estimate of the vibrational parameters omega(e)" and omega(e)"-CHI(e)".
A new confocal scanning beam transmission and reflection microscope is described. The new microscope uses the same detector for both transmitted-light and reflected-light images. The transmitted beam is re-injected in...
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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.
The QED fermion self-energy and vertex functions are calculated for general values of the gauge parameter ξ with the unified-gauge formalism for axial-type gauges. The Ward identity is verified and the results are co...
The QED fermion self-energy and vertex functions are calculated for general values of the gauge parameter ξ with the unified-gauge formalism for axial-type gauges. The Ward identity is verified and the results are compared with the corresponding expressions in the Coulomb gauge and Feynman gauge.
The development of smectic-A ordering at the interface between isotropic liquid and vapor is studied using a density-functional theory, based on a mean-field approximation for the effect of attractive pair interaction...
The development of smectic-A ordering at the interface between isotropic liquid and vapor is studied using a density-functional theory, based on a mean-field approximation for the effect of attractive pair interactions and weighted-density treatment of repulsive-core contributions. In contrast to earlier microscopic theories of this phenomenon, the bulk liquid and vapor phases are in complete coexistence with each other, and no arbitrary ‘‘surface fields’’ independent of molecular pair interactions are invoked. The wetting behavior of the interface is studied as a function of the molecular-core anisotropy, which controls the relative stability of bulk nematic and smectic-A phases, under conditions where the attractive pair interactions favor complete wetting by the nematic phase. There is a change to incomplete wetting by the smectic-A phase when the latter preempts the nematic, in a process analogous to a triple-point wetting transition. This is consistent with experimental results, but the growth of smectic layers at the interface is always found to be continuous, with no evidence of the first-order layering transitions observed in experiment.
In this paper, a two-dimensional model for water-oil-surfactant mixtures, previously studied by the Monte Carlo method, is now investigated by examining (4×∞) strips of the lattice using the transfer-matrix meth...
In this paper, a two-dimensional model for water-oil-surfactant mixtures, previously studied by the Monte Carlo method, is now investigated by examining (4×∞) strips of the lattice using the transfer-matrix method. The correlation and structure functions in the disordered phase are calculated accurately, as demonstrated by comparison with Monte Carlo results. We find the behavior of these functions to be similar to their counterparts on the more realistic three-dimensional lattice, justifying the use of two-dimensional lattices for studying the disordered phase. From these functions we calculated the disorder and Lifshitz lines which are used to divide the disordered phase into a region of ordinary fluid and a region of microemulsion. We also illustrate that two-dimensional models may not be able to produce the three-phase coexistence between microemulsion, the water-rich phase, and the oil-rich phase obtained with three-dimensional models.
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