197 research outputs found
Effect of pressure on the polarized infrared optical response of quasi-one-dimensional LaTiO
The pressure-induced changes in the optical properties of the
quasi-one-dimensional conductor LaTiO were studied by
polarization-dependent mid-infrared micro-spectroscopy at room temperature. For
the polarization of the incident radiation parallel to the conducting
direction, the optical conductivity spectrum shows a pronounced mid-infrared
absorption band, exhibiting a shift to lower frequencies and an increase in
oscillator strength with increasing pressure. On the basis of its pressure
dependence, interpretations of the band in terms of electronic transitions and
polaronic excitations are discussed. Discontinuous changes in the optical
response near 15 GPa are in agreement with a recently reported pressure-induced
structural phase transition and indicate the onset of a dimensional crossover
in this highly anisotropic system.Comment: 7 pages, 7 figure
Raman scattering in osmium under pressure
The effect of pressure and temperature on the Raman-active phonon mode of
osmium metal has been investigated for pressures up to 20 GPa and temperatures
in the range 10--300 K. Under hydrostatic conditions (He pressure medium) the
phonon frequency increases at a rate of 0.73(5) cm^{-1}/GPa (T = 300 K). A
large temperature-induced and wavelength-dependent frequency shift of the
phonon frequency is observed, of which only a small fraction can be associated
with the thermal volume change. The main contribution to the temperature
dependence of the phonon frequency is rather attributed to non-adiabatic
effects in the electron-phonon interaction, which explains also the observation
of an increasing phonon line width upon cooling. The phonon line width and the
pressure-induced frequency shift were found to be unusually sensitive to shear
stress.Comment: 4 pages, 2 figure
Plasmons in Sodium under Pressure: Increasing Departure from Nearly-Free-Electron Behavior
We have measured plasmon energies in Na under high pressure up to 43 GPa
using inelastic x-ray scattering (IXS). The momentum-resolved results show
clear deviations, growing with increasing pressure, from the predictions for a
nearly-free electron metal. Plasmon energy calculations based on
first-principles electronic band structures and a quasi-classical plasmon model
allow us to identify a pressure-induced increase in the electron-ion
interaction and associated changes in the electronic band structure as the
origin of these deviations, rather than effects of exchange and correlation.
Additional IXS results obtained for K and Rb are addressed briefly.Comment: 5 pages, 4 figure
Calculated elastic and electronic properties of MgB at high pressures
The effect of high pressure on structural and electronic properties of the
novel superconductor \MB has been calculated using the full-potential
linearized augmented-plane-wave method. Despite the layered crystal structure
of \MB nearly isotropic compression (bulk modulus GPa) is found
with only a 1.2% decrease of the ratio at 10 GPa. The effect of pressure
on the critical temperature has been estimated on the basis of BCS theory and
good agreement with experimental data is found. Our results suggest that it is
a combination of increasing phonon frequency and decreasing electronic density
of states at the Fermi level which leads to the observed decrease of the
critical temperature under pressure.Comment: 10 pages, 3 figures (EPS), Elsevier LaTeX. More detailed analysis of
the pressure dependence of Tc; results unchanged. Manuscript accepted for
publication in Solid State Commu
Crystal structure of LaTiO_3.41 under pressure
The crystal structure of the layered, perovskite-related LaTiO_3.41
(La_5Ti_5O_{17+\delta}) has been studied by synchrotron powder x-ray
diffraction under hydrostatic pressure up to 27 GPa (T = 295 K). The
ambient-pressure phase was found to remain stable up to 18 GPa. A sluggish, but
reversible phase transition occurs in the range 18--24 GPa. The structural
changes of the low-pressure phase are characterized by a pronounced anisotropy
in the axis compressibilities, which are at a ratio of approximately 1:2:3 for
the a, b, and c axes. Possible effects of pressure on the electronic properties
of LaTiO_3.41 are discussed.Comment: 5 pages, 6 figure
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