Energy Spectrum Of Elementary Excitations Research Articles

Energy Spectrum of Elementary Excitations of Electron Liquid of Conductors in Magnetic Field (II).

Energy Spectrum of Elementary Excitations of Electron Liquid of Conductors in Magnetic Field (II).

Charged-boson fluid at zero-temperature in the fractional dimensional space

In the fractional dimensional space, the ground state properties of the charged-boson fluid are studied in a theory which goes beyond the random phase approximation by including correlations through a static local-field-factor. The structure factor and static local field-factor are obtained in the self-consistent method. Qualitative agreement with the Monte Carlo results on static screening is achieved by imposing self-consistency on the compressibility of the fluid in addition to self-consistency on the structure factor. Using the structure factors obtained in these methods, several properties of the charged boson system such as the energy spectrum of elementary excitations, the pair-correlation function, the ground state energy, the pressure, the chemical potential and the compressibility are obtained in several dimensions including both integer and fractional values. Results obtained in the later method in two and three dimensional systems are close to the Monte Carlo and hypernetted-chain methods. The Wigner crystallisation in the lower dimensional system is found at higher density of bosons. However, it vanishes in any lower dimensional system whose dimension lies below 2.

Static and dynamic properties of a two-dimensional charged Bose fluid

We investigate some static and dynamic properties of a two-dimensional charged Bose fluid interacting via ln (r) potential by using the self-consistent-field approximation of Singwi, Tosi, Land, and Sj\"olander. The static structure factor, the pair-correlation function, the energy spectrum of elementary excitations, and the static dielectric-response function are calculated over a wide density range (1\ensuremath{\leqslant}${\mathrm{r}}_{\mathrm{s}}$\ensuremath{\leqslant}10). Wherever available, the results for the structure factor are compared with the recent diffusion Monte Carlo calculation by Magro and Ceperley and a good agreement is found. A comparison is also made with the two-dimensional charged Bose fluid with 1/r interaction potential. It is noticed that the Bose fluid interacting with ln (r) potential becomes partially localized at ${\mathrm{r}}_{\mathrm{s}}$\ensuremath{\approx}10, which is closer to the Monte Carlo prediction of Wigner crystallization at ${\mathrm{r}}_{\mathrm{s}}$\ensuremath{\approx}12.

Energy spectrum and hydrodynamics of superfluid He II in a strong electric field

A strong electric field changes the energy spectrum of elementary excitations in superfluid helium and makes it anisotropic. It is shown that the electric field influences the superfluid hydrodynamics as well, diminishing the superfluid current orthogonal to the field.

Charged Bose gas atT=0

The ground state of a charged Bose gas is studied throughout a large range of densities in a self-consistent-field approximation formalism which includes the short-range correlations between bosons through a local-field correction. Numerical self-consistent calculations have been carried out in order to determine the static structure factor $S(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$. Hence, from $S(\stackrel{\ensuremath{\rightarrow}}{\mathrm{q}})$ we have obtained the pair-correlation functions, the ground-state energy which essentially is the correlation energy, the pressure of the gas, and, from Feynman's relation, the energy spectrum of elementary excitations. The response of the system to a static impurity charge has also been investigated. In the high-density limit our calculations show the same results as those given by Bogoliubov's perturbation theory. In the intermediate-density region, corresponding to the strongly coupled system, our results are in very good agreement with recent calculations based on the hypernetted-chain integral equation as well as Monte Carlo computations.

Excitation spectrum of a system of interacting bosons

The Bogoliubov treatment of a weakly interacting Bose gas is extended by allowing macroscopic occupation of many single-particle quantum states. This generalization of having more than a single condensed mode gives rise to a nonuniform condensate and is being considered as a possible mechanism for the description of a dense strongly interacting Bose gas at low temperatures. The model with a repulsive $\ensuremath{\delta}$-function interparticle potential gives an energy spectrum of elementary excitations or quasiparticles with both phonon and roton features. The values obtained for the roton minimum energy $\ensuremath{\Delta}$ and the speed of (first) sound agree reasonably well with inelastic-neutron-scattering data.

Brillouin-Wigner perturbation procedure for elementary excitations in liquidHe4

The energy spectrum of elementary excitations in liquid $^{4}\mathrm{He}$ is studied using the Brillouin-Wigner (BW) perturbation formalism in conjunction with the method of correlated basis functions. Phonon functions and interaction matrix elements associated with three- and four-phonon vertices are derived. Iteration of the BW energy series is carried out by including: (i) two one-ring types of second-order energy corrections evaluated with the inclusion of the leading correction to the convolution approximation for the three-particle distribution function, and (ii) six two-ring types of second-, third-, and fourth-order perturbation energies obtained with the use of the convolution approximations for the three- and four-particle distribution functions. The entire formulation is developed in terms of the liquid-structure function generated by the optimum Bijl-Dingle-Jastrow type of trial wave function. The resulting energy spectrum is found to agree with experimental results more closely than many earlier theoretical calculations.

Exciton-like excitations in liquid helium

The energy spectrum of elementary excitations in superfluid helium is derived on the basis of arguments based on a model for the liquid structure. The spectrum consists of two branches: the Landau-Feynman branch and a new branch, above the Landau-Feynman branch, whose central part has been observed experimentally by Iwamoto.

Long-wavelength-phonon spectrum in liquidHe4

The energy spectrum of elementary excitations in liquid $^{4}\mathrm{He}$ is studied in the long-wavelength limit by means of the Brillouin-Wigner (BW) perturbation theory for two-phonon processes. Calculation of an additional second-order BW energy correction to the Bijl-Feynman excitation spectrum is carried out by considering contributions from the leading correction to the convolution approximation for the three-particle distribution function. The resulting correction is found to be positive and about 7.9% of the second-order perturbation energy obtained previously with the convolution approximation.

Energy Spectrum of Elementary Excitations in a Boson Fluid

The Bogoliubov-Zubarev method of collective coordinates is used to derive the energy spectrum of elementary excitations in a weakly interacting many-boson system through second-lowest order in a weak coupling expansion. The obtained result of the spectrum is shown to be equivalent to that evaluated by means of the variation-perturbation procedure based on the method of correlated basis functions in the uniform limit. Comparison of the excitation spectrum is also made briefly with two other results calculated using the Bogoliubov-Zubarev Hamiltonian in somewhat related but different approaches.

Three-phonon vertex corrections to the excitation spectrum and liquid-structure function of liquid4He

The energy spectrum of elementary excitations and the liquid-structure function of liquid4He are calculated by means of the method of correlated basis functions in the approximation of second-order perturbation theory. The procedure is based on (i) the construction of phonon functions in terms of collective coordinates and the optimum Bijl-Dingle-Jastrow type of ground-state wave function and (ii) the evaluation of leading correction terms to the Bijl-Feynman excitation spectrum, which are generated by two types of three-phonon vertices. Numerical results are obtained using the optimum liquid-structure function computed by Campbell and Feenberg in the paired-phonon analysis.

The interaction of excitons in the superliquid state with phonons in molecular crystals

The energy spectrum of excitons in the superliquid state has been investigated in interaction with phonons in molecular crystals. The corresponding branches of the energy spectrum of elementary excitations have been determined and the effect of the interaction with phonons on their stability has been investigated and discussed. The possibility of the resonance excitation of hydrons by means of phonons is discussed.

Superliquid state of an exciton mixture with small exciton radii in molecular crystals

The energy spectrum of excitons with a small radius in a superliquid state in molecular crystals has been investigated. A more complicated structure of the exciton energy spectrum with a number of equivalent minima for k ≠ 0 has been considered. The problem was solved as that of determining the energy spectrum of a mixture of various types of non-ideal exciton gases in a superliquid state, corresponding to the individual exciton energy minima. The appropriate branches of the energy spectrum of elementary excitations (hydrons) have been determined and the conditions for their stability have been investigated.

Energy Spectrum of Elementary Excitations in Liquid Helium

Energy Spectrum of Elementary Excitations in Liquid Helium

Energy Spectrum of Elementary Excitations in Helium II

The contribution of phonon-phonon interactlon to the energy of elementary excitations in liquid He/sub 4/ is evaluated in the approximation of the Brillouin-Wigner second order energy. The three-particle distribution function p(1,2,3) occurring in the interaction matrix elements is approximated by the Kirkwood superposition form and also by the convolution'' form. A generai criterion is developed to test the accuracy of possible approximations for p(1,2,3). The criterion has the form of a functional X in p(1,2,3) which vanishes if p(1,2,3) is generated by the correct ground state solution of the Schrodinger equation. If an approximate form is used the corresponding functional X/sub a/ does not vanish and thus provides a measure of accuracy. The power of this criterion resides in the fact that X/sub a/ is a function of three variabies, the magnitudes of two wave vectors and the cosine of the angle between them. The computed dispersion curves are compared with the experimental curve constructed by Henshaw and Woods from the inelastic single scattering of slow neutrons in liquid helium (auth)