Phonon density of states and compression behavior in iron sulfide under pressure

We report the partial phonon densities of states (DOS) of iron sulfide, a possible component of the rocky planet's core, measured by the 57Fe nuclear resonant inelastic x-ray scattering and calculate the total phonon DOS under pressure. From the phonon DOS, we drive thermodynamic parameters. A comparison of the observed and estimated compressibilities makes it clear that there is a large pure electronic contribution in the observed compressibility in the metallic state. Our results present the observation of thermodynamic parameters of iron sulfide with the low-spin state of an Fe2+ ion at the high density, which is similar to the condition of the Martian core.     

Phonon density of states of ann-component alloy

We have generalized the coherent potential approximation (CPA) of Tripathi and Behera to the case of ann-component alloy. It is seen that then-component CPA density of states reproduces the binary, ternary quartenary alloys etc when the appropriate limits are adopted.     

Phonon density of states of single-wall carbon nanotubes

The vibrational density of states of single-wall carbon nanotubes (SWNT) was obtained from inelastic neutron scattering data from 0 to 225 meV. The spectrum is similar to that of graphite above 40 meV, while intratube features are clearly observed at 22 and 36 meV. An unusual energy dependence below 10 meV is assigned to contributions from intertube modes in the 2D triangular lattice of SWNT bundles, and from intertube coupling to intratube excitations. Good agreement between experiment and a calculated density of states for the SWNT lattice is found over the entire energy range.     

Phonon density of states of tetracyanoethylene from coherent inelastic neutron scattering at Dhruva reactor

Inelastic neutron scattering experiments to determine phonon density of states of coherent scattering samples of polycrystalline complex solids are generally intensity-limited and therefore are feasible only at high flux facilities. Phonon density of states of the monoclinic phase of tetracyanoethylene at 300 K, obtained using the medium resolution triple axis spectrometer at the new Indian medium flux reactor Dhruva are reported here. The raw data is converted to the “neutron weighted” phonon density of states by applying suitable corrections. Comparison made with results from a theoretical calculation based on a semirigid molecule model of lattice dynamics is fair. Results from Dhruva are also consistent with that obtained (to be published) at the high flux pulsed neutron source (ISIS) of the Rutherford Appleton Laboratory in United Kingdom.     

Phonon density of states of V3Si

The phonon density of states of V₃Si at 300°K has been calculated from a microscopic model. It exhibits three pronounced peaks, in qualitative agreement with experimental results of Schweiss obtained from inelastic neutron scattering. By reducing the effective charges of both ions the agreement can be improved, but at the expense of agreement for the mode softening.     

Quasi-two-dimensional metallic hydrogen in diphosphide at a high pressure

The average optical reflectivity of bismuth as a function of time t after irradiation by a short laser pulse has been calculated. The amplitude A of photoinduced oscillations in the average optical reflectivity is shown to have extrema under certain conditions. The time τ_j (j is a natural number) at which the amplitude A reaches the jth extremum has been calculated. The calculated dependences of the times τ₁ and τ₂ at which, respectively, the first and second extrema (the first minimum and the first maximum) of the amplitude A are reached on the maximum laser pulse energy density Q are consistent with the experimental data from [8].     

Phonon density of states of LaFeAsO(1-x)Fx

We have studied the phonon density of states (PDOS) in LaFeAsO(1-x)Fx with inelastic neutron scattering methods. The PDOS of the parent compound (x=0) is very similar to the PDOS of samples optimally doped with fluorine to achieve the maximum Tc (x approximately 0.1). Good agreement is found between the experimental PDOS and first-principles calculations with the exception of a small difference in Fe mode frequencies. The PDOS reported here is not consistent with conventional electron-phonon mediated superconductivity.     

Phonon density of states and phonon dispersion of superconducting MgB2

For the superconductor MgB2, we have calculated the phonon density of states (DOS), phonon dispersion and Eliashberg function throughout the Brillouin zone (BZ), using an empirical potential model. The calculated values are consistent with the theoretical and experimental values. The calculated results show our empirical potential model is available for MgB2.     

Phonon density of states and phonon dispersion of superconducting MgB2

For the superconductor MgB2, we have calculated the phonon density of states （DOS）, phonon dispersion and Eliashberg function throughout the Brillouin zone （BZ）, using an empirical potential model. The calculated values are consistent with the theoretical and experimental values. The calculated results show our empiricalpotential model is available for MgB2.     

Electronic density of states of high pressure liquid uranium from shock vaporization

Strong shock waves were used to compress and heat initially porous uranium plates to high pressures (≈10⁶atm) and temperatures high enough (some 10⁴K), that one should expect a dominant contribution of the electrons to the thermal state. Information about this contribution, which depends on the electronic density of states distribution D(E), is obtained by measuring the entropy in the shocked state on the basis of the shock vaporization technique. The results indicate that a considerable redistribution of the six valence electrons occurs when uranium is compressed and heated.     

Phonon dispersion of zinc chalcogenides under extreme pressure and the metallic transformation

The effect of high pressure on the one- and two-phonon Raman spectra of ZnTe, ZnSe, and ZnS has been measured up to their metallic phase transitions, at 95, 137, and 150 kbar respectively. Zone boundary transverse acoustic phonons “soften” with pressure in each case. For ZnTe, ZnSe, ZnS, Si, and GaP a linear correlation is found between the mode Grüneisen parameters for TA(X) and the transition pressures.     

Phonon linewidths of NaF at high temperatures

The linewidths of transverse acoustic modes in NaF are calculated for temperatures up to the melting point. We show that the widths decrease in a certain long wavelength region with increasing temperatures. The results are compared with recent neutron experiments up to 700 K.     

The role of electronic density of states in metallic Lanthanum

Observations of X-ray photoabsorption in metallic Lanthanum in the vicinity of the 3d _5/2-edge are given. Two separated absorption peaks are detected at the quantum energies =830.6eV and =834.0eV. The results are interpreted according to the model given in communication I–IV [1].     

Phonon emission spectra of thin metallic films

Thin metallic films evaporated on an Al₂O₃-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.     

Smoothness of the density of states in the Anderson model at high disorder

We prove smoothness of the density of states in the Anderson model at high disorder for a class of potential distributions that include the uniform distribution.Research partially supported by the NSF under grants DMS 83-01889 and INT 85-03418Research partially supported by the CNPq