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Thomas F George - One of the best experts on this subject based on the ideXlab platform.
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variational density matrix approach to the temperature dependent Elementary Excitation spectrum of two dimensional liquid 4 he
Journal of Low Temperature Physics, 1996Co-Authors: Chungin Um, Jaerok Kahng, Kyuhwang Yeon, Thomas F GeorgeAbstract:Using the variational density matrix method, we obtain a temperature-dependent Elementary Excitation spectrum for two-dimensional liquid4He. For more precise results, we use a Jastrow-Feenberg-type trial wave function and include the contribution of Elementary diagrams within the hypernetted chain approximation. The behavior of the Excitation spectrum as a function of the temperature and density in two dimensions is similar to that of the bulk system, but has a smaller roton minimum. The roton minimum of the Excitation spectrum decreases with increasing temperature and increases with increasing density at low densities but decreases at large densities. The results agree well with Monte Carlo calculations and are closer than pevious theories to experimental measurements of4He film adsorbed on substrates.
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temperature variation of the Elementary Excitation spectrum of two and three dimensional liquid 4he
Physica B-condensed Matter, 1995Co-Authors: Chungin Um, Thomas F GeorgeAbstract:Adopting the separability assumption in conjunction with the hypernetted-chain approximation and the minimum principle of Helmholtz free energy based on the trial density matrix expressed in terms of Jastrow-type wave functions, a set of coupled Euler-Lagrange equations are obtained for the radial distribution function, structure function, Excitation spectrum and occupation number of a quantum fluid at finite temperatures. Numerical solutions of these functions are determined through a generalization of the linearized variational calculation method. The behavior of these functions as the temperature and density is varied in two dimensions is similar to three-dimensional experimental data.
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thermal conductivity and first viscosity via temperature dependent Elementary Excitation spectra in thin and bulk liquid 4he
Physica B-condensed Matter, 1994Co-Authors: Chungin Um, Thomas F George, Lakshmi N PandeyAbstract:Abstract The coefficients of thermal conductivity (ϰ) and first viscosity (η) in thin and bulk liquid 4 He are evaluated explicitly as a function of temperature via the zero-temperature and temperature-dependent two- and three-dimensional Elementary Excitation spectra that are microscopic only in the long-wavelength limit. The coefficients ϰ( T ) and η( T ) obtained from the temperature-dependent spectrum have slightly larger values than those of the zero-temperature spectrum through the whole range of temperatures, while as the temperature approaches absolute zero, the coefficients ϰ( T ) and η( T ) coincide with each other in both spectra. Below about 0.8 K, both coefficients increase exponentially with decreasing temperature. At temperatures below about 0.3 K, ϰ( T ) in the thin and bulk cases have T -5 and T -6 dependences, respectively, whereas η ph ( T ) has a T -1 dependence in both dimensions with extra temperature-dependent terms, which originate from three-phonon processes for both Excitation spectra.
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temperature variation of the Elementary Excitation spectrum of thin liquid 4he films
Physical Review B, 1992Co-Authors: Chungin Um, Thomas F GeorgeAbstract:Abstract : The temperature variation of the Elementary Excitation spectrum of thin liquid (4)He films is derived within the ring diagram approximation. This theory is microscopic only in the long wavelength limit. Using this anomalous spectrum, the specific heat data adsorbed on Grafoil graphite and the first, second and third sounds are analyzed. The temperature variation of the phonon spectrum is very negligible for low temperatures. However, with increasing temperature from 0.6 - 0.7 K to near the vicinity of the two-dimensional transition temperature of 1-.21 K, the temperature effect is significant regarding the physical properties of thin liquid (4)He films.
Ayao Okiji - One of the best experts on this subject based on the ideXlab platform.
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Elementary Excitation for the orbitally degenerate anderson model at finite temperatures
Physical Review B, 2000Co-Authors: A Tomiyama, S Suga, Ayao OkijiAbstract:The Elementary Excitation for the orbitally degenerate Anderson model at finite temperatures is studied using the Bethe ansatz solution. The formulation of the Elementary Excitation at finite temperatures is based on the method which was first developed by Yang and Yang for the one-dimensional boson system with the $\ensuremath{\delta}$-function type interaction. The expressions of the Elementary Excitation energy for the spin and the charge degrees of freedom are derived. Using the obtained expressions, the spin and the charge Excitation spectrums are calculated numerically. With decreasing temperature, the peak structure grows in the spin Excitation spectrum, whereas the weight around the impurity level increases in the charge Excitation spectrum, below the temperature corresponding to the characteristic energy scale of the system. The crystalline-field effects on the Elementary Excitation spectrums are investigated in the Kondo regime, and the results are discussed in connection with the difference in the Kondo temperature. The relation between the obtained results and the thermodynamic quantity of the orbitally degenerate Anderson model is also discussed.
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Elementary Excitations for the Anderson model at finite temperatures
European Physical Journal B, 1998Co-Authors: A Tomiyama, Sei-ichiro Suga, Ayao OkijiAbstract:The Elementary Excitation spectrums for the Anderson model at finite temperatures are calculated by using the Bethe-ansatz solution. The formulation is based on the method of Yang and Yang, which was developed for the one-dimensional boson systems with the \(\)-function type interaction. We obtain the temperature dependence of the spin and the charge Excitation spectrums. When the impurity level lies deeply from the Fermi level and the Coulomb interaction is suitably large, the resonant peak structure develops in the low energy region of the spin Excitation spectrum and the hump structure grows around the impurity level of the charge Excitation spectrum with decreasing temperature.
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Elementary Excitations for the integrable spin- S Heisenberg chain with an impurity spin
Journal of Physics: Condensed Matter, 1996Co-Authors: Y Morita, S Suga, Ayao OkijiAbstract:Elementary Excitations for the integrable spin-S antiferromagnetic Heisenberg chain with an impurity spin are investigated by using the Bethe ansatz solution. Dressed holes are introduced in order to describe the Elementary Excitation. The characteristic energy dependence of the spectral density for the Elementary Excitation at zero temperature is discussed in connection with behaviour patterns of physical quantities. We extend our calculation for the Elementary Excitation to the case of finite temperatures, applying the method developed by Yang and Yang for one-dimensional interacting boson systems. At finite temperatures, in the case where , the spectral density shows a divergence property at zero Excitation energy irrespective of the temperature, whereas in the case where , the peak structure develops in the low-energy region as the temperature is decreased.
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Elementary Excitation spectrum for the multichannel kondo model at finite temperatures
Physical Review B, 1994Co-Authors: S Suga, Ayao Okiji, Norio KawakamiAbstract:Spectral density for the Elementary Excitation of the multichannel Kondo model is investigated at finite temperatures with the use of the Bethe-ansatz method. Our formulation is based on the method of Yang and Yang developed in one-dimensional interacting boson systems. In the orbital singlet case, the narrow peak structure develops in the low-energy region as the temperature is decreased, whereas in the underscreened case, the Excitation spectrum exhibits a divergence property at zero Excitation energy, irrespective of the temperature. In the overscreened case, in which the non-Fermi-liquid fixed point is stable in the ground state, the peak structure develops in the low-energy region and the weight at zero Excitation energy increases as the temperature is decreased. We discuss characteristic properties of the Excitation spectrum in connection with bulk properties.
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Elementary Excitation spectra in the s d model at finite temperatures
Journal of the Physical Society of Japan, 1992Co-Authors: M Yamashita, Ayao Okiji, Norio KawakamiAbstract:Elementary Excitations in the s-d model are calculated at finite temperatures with the use of the Bethe-ansatz solution. Our formulation of the spectra is based on Yang and Yang's method which has been developed in the one-dimensional interacting boson system. We investigate the temperature dependence of the spin Excitation spectra. It is shown that the narrow peak structure develops in the low energy region as the temperature is decreased. At low temperatures, the shape of the spectra is described well by the renormalized resonance level model.
M Bellini - One of the best experts on this subject based on the ideXlab platform.
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single photon Excitation of a coherent state catching the Elementary step of stimulated light emission
Physical Review A, 2005Co-Authors: Alessandro Zavatta, Silvia Viciani, M BelliniAbstract:When a single quantum of electromagnetic field Excitation is added to the same spatiotemporal mode of a coherent state, a new field state is generated that exhibits intermediate properties between those of the two parents. Such a single-photon-added coherent state is obtained by the action of the photon creation operator on a coherent state and can thus be regarded as the result of the most Elementary Excitation process of a classical light field. Here we present and describe in depth the experimental realization of such states and their complete analysis by means of a novel ultrafast, time-domain, quantum homodyne tomography technique clearly revealing their nonclassical character.
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catching the Elementary step of Excitation of a coherent light state by a single photon
Proceedings of SPIE, 2005Co-Authors: M Bellini, Alessandro Zavatta, Silvia VicianiAbstract:A new class of non-classical light states has been experimentally generated and their complete phase-space characterization has been achieved by quantum homodyne tomography. Such states are produced by the action of the photon creation operator on a coherent light field and are thus the result of the Elementary Excitation process of a classical field by a single quantum. Being intermediate between a single-photon Fock state and a coherent one, they offer the unique opportunity to closely follow the smooth evolution between the particle-like and the wave-like behavior of the light field.
T P Devereaux - One of the best experts on this subject based on the ideXlab platform.
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uncovering selective Excitations using the resonant profile of indirect inelastic x ray scattering in correlated materials observing two magnon scattering and relation to the dynamical structure factor
New Journal of Physics, 2012Co-Authors: Chengchien Chen, A P Sorini, Brian Moritz, T P DevereauxAbstract:Resonant inelastic x-ray scattering (RIXS) is a spectroscopic technique that has been widely used to study various Elementary Excitations in correlated and other condensed matter systems. For strongly correlated materials, besides boosting the overall signal the dependence of the resonant profile on incident photon energy is still not fully understood. Previous endeavors in connecting indirect RIXS, such as Cu K-edge where scattering takes place only via the core–hole created as an intermediate state, with the charge dynamical structure factor S(q,ω) neglected complicated dependence on the intermediate state configuration. To resolve this issue, we performed an exact diagonalization study of the RIXS cross-section using the single-band Hubbard model by fully addressing the intermediate state contribution. Our results are relevant to indirect RIXS in correlated materials, such as high-Tc cuprates. We demonstrate that RIXS spectra can be reduced to S(q,ω) when there is no screening channel for the core–hole potential in the intermediate state. We also show that two-magnon Excitations are highlighted at the resonant photon energy when the core–hole potential in the corresponding intermediate state is poorly screened. Our results demonstrate that different Elementary Excitations can be emphasized at different intermediate states, such that selecting the exact incident energy is critical when trying to capture a particular Elementary Excitation.
Gilbert Grynberg - One of the best experts on this subject based on the ideXlab platform.
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Radiation Pressure in a Rubidium Optical Lattice: An Atomic Analog to the Photorefractive Effect
Physical Review Letters, 1997Co-Authors: Samuel Guibal, C. Mennerat-robilliard, C. Triché, D. Larousserie, J.-y. Courtois, Gilbert GrynbergAbstract:Probe gain in a rubidium optical lattice is observed when the probe and lattice beams have identical frequencies. This effect is shown to arise from the radiation pressure that shifts the atomic density distribution with respect to the optical potential. This effect is compared with two-beam coupling in photorefractive materials. The experimental results obtained by changing the parameters of the optical lattice (intensity, detuning, periodicity) are in reasonable agreement with numerical simulations based on the model case of a 12 ! 32 atomic transition. [S0031-9007(97)03427-3] PACS numbers: 32.80.Pj, 32.60. + i, 42.65.Hw Two-beam coupling [1] between frequency-degenerate laser beams is one of the most intriguing phenomena in nonlinear optics. Owing to the apparent symmetry of the interaction between two such beams and a nonlinear medium, one indeed expects no net power transfer to take place between the laser waves. Of course, the symmetry can be broken through the intensity, direction, or polarization of the beams. Still, the possibility of observing an actual amplification of one wave at the expense of the other is a rather uncommon phenomenon. This can be better understood by identifying the conditions required in such a process. The intensity attenuation or amplification of a laser beam during propagation through a material medium arises from the existence of a macroscopic polarization (i) having the same characteristics (frequency and wave vector) as the incident beam, (ii) but having a p2 phase-shifted component with respect to this beam. In the more particular case of two-beam coupling where the intensity modification only occurs in the presence of a supplementary beam, the polarization of interest is necessarily non-linear in nature. Although nonlinear interactions naturally provide polarization components fulfilling requirement (i) through the creation of gratings in the material medium by the interference pattern between the incident waves, condition (ii) is very seldom fulfilled because, most generally, a stationary interference pattern (the incident laser beams have the same frequency) can only induce 0 or p phase-shifted steady-state material gratings. The photorefractive effect [2] taking place in some particular crystals such as LiNbO 3 or BaTiO 3 is one (if not the only) outstanding counterexample of this intuitive general property. In such crystals, the spatially modulated intensity distribution Ir due to the interference between the two incident beams generates charge carriers in the conduction band through photoExcitation, at a rate proportional to the local value of the optical intensity. Because of spatial diffusion through the crystal, the carriers migrate towards points of smaller intensity where they re-combine with donors. This results in a charge density rr exhibiting a p phase shift with respect to Ir. Because of the Poisson equation [ ? ´E r], the spatially varying charge distribution rr gives rise to a nonuniform electric field Er, which is phase shifted p2 with respect to Ir. Finally, Er yields a proportional refractive index grating nr through the linear electro-optic effect (Pockels effect). Thus, by transforming an incident interference pattern Ir into a p2 phase-shifted grating nr, the photorefractive effect allows power exchange between frequency-degenerate laser beams [3]. In this Letter, we present and experimentally demonstrate an analog of this seemingly very peculiar effect in the case of an atomic gaseous medium. More precisely, we show that the transmission spectrum of a weak probe beam interacting with a standard three-dimensional lin lin optical lattice [4] can display a narrow Lorentzian-like central resonance. The probe gain in the frequency-degenerate regime can reach up to 10% and can be interpreted as a two-beam coupling process involving the creation of an atomic density (or equivalently a refractive index) grating phase shifted p2 with respect to the stationary probe-lattice wave. We show that this phenomenon arises from the radiation pressure exerted by the probe-lattice pattern onto the atoms. This proves that the dissipative forces, although generally neglected, can have a dramatic effect on the spatial distribution of atoms in optical lattices. Furthermore , we show that the width of the central resonance is related to the spatial diffusion tensor [5] of the atoms in the lattice, which can thus be investigated directly. Standard four-beam optical lattices [4] consisting of two x-polarized beams propagating in the yOz plane and making an angle 2u y , and two y-polarized beams propagating in the xOz plane and making an angle 2u x [see Fig. 1(a)], have been intensively investigated during the last few years. Many properties of this system have been already revealed: oscillating motion of the atoms in the optical potential wells associated with the light shifts [6,7], narrowing of the vibrational lines due to strong spatial confinement at the bottom of the wells [8], para-magnetic behavior [9], long range spatial order [10], propagating Elementary Excitation modes [11], etc. Curiously 0031-90079778(25)4709(4)$10.00
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propagating Elementary Excitation in a dilute optical lattice
Physical Review Letters, 1996Co-Authors: J.-y. Courtois, Samuel Guibal, D R Meacher, P Verkerk, Gilbert GrynbergAbstract:Propagating Elementary Excitations characterized by a well-defined propagation velocity (such as acoustic waves) are usually considered as being typical of condensed matter or dense fluids. We show that this requirement is actually not necessary. We predict in the case of a dilute optical lattice the occurrence of a propagating Excitation mode which can induce a stimulated scattering mechanism analogous to stimulated Brillouin scattering, although it does not involve any interaction between atoms. We also present the results of an experimental investigation in cesium that demonstrates the existence of this novel stimulated scattering process. {copyright} {ital 1996 The American Physical Society.}