992 research outputs found
Deconfinement transition and dimensional crossover in the Bechgaard-Fabre salts: pressure- and temperature-dependent optical investigations
The infrared response of the organic conductor (TMTSF)PF and the Mott
insulator (TMTTF)PF are investigated as a function of temperature and
pressure and for the polarization parallel and perpendicular to the molecular
stacks. By applying external pressure on (TMTTF)PF, the Mott gap
rapidly diminishes until the deconfinement transition occurs when the gap
energy is approximately twice the interchain transfer integral. In its
deconfined state (TMTTF)PF exhibits a crossover from a
quasi-one-dimensional to a higher-dimensional metal upon reducing the
temperature. For (TMTSF)PF this dimensional crossover is observed
either with increase in external pressure or with decrease in temperature. We
quantitatively determine the dimensional crossover line in the
pressure-temperature diagram based on the degree of coherence in the optical
response perpendicular to the molecular stacks.Comment: 12 pages, 15 figure
The Expeditions PS139/1 and PS139/2 of the Research Vessel POLARSTERN to the Atlantic Ocean in 2023
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
The Expeditions PS130/1 and PS130/2 of the Research Vessel POLARSTERN to the Atlantic Ocean in 2022
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
Structural investigations on -FeGe at high pressure and low temperature
The structural parameters of -FeGe have been determined at ambient
conditions using single crystal refinement. Powder diffraction have been
carried out to determine structural properties and compressibility for
pressures up to 30 GPa and temperatures as low as 82 K. The discontinuous
change in the pressure dependence of the shortest Fe-Ge interatomic distance
might be interpreted as a symmetry-conserving transition and seems to be
related to a magnetic phase boundary line.Comment: 4 pages, 5 figure
Anisotropic compression in the high pressure regime of pure and Cr-doped vanadium dioxide
We present structural studies of VCrO (pure, 0.7% and 2.5% Cr
doped) compounds at room temperature in a diamond anvil cell for pressures up
to 20 GPa using synchrotron x-ray powder diffraction. All the samples studied
show a persistence of the monoclinic symmetry between 4 and 12 GPa. Above
12 GPa, the monoclinic symmetry changes to isostructural phase
(space group ) with a significant anisotropy in lattice compression of
the - plane of the phase. This behavior can be reconciled
invoking the pressure induced charge-delocalization
High-Pressure Phase Transition of the Oxonitridosilicate Chloride Ce4[Si4O3+xN7-x]Cl1-xOx with x = 0.12 and 0.18
The high-pressure behaviour of the oxonitridosilicate chlorides Ce4[Si4O3þxN7-x]Cl1-xOx, x = 0.12 and 0.18, is investigated by in situ powder synchrotron X-ray diffraction. Pressures up to 28 GPa are generated using the diamond-anvil cell technique. A reversible phase transition of first order occurs at pressures between 8 and 10 GPa. Within this pressure range the high- and the low-pressure phases are observed concomitantly. At the phase transition the unit cell volume is reduced by about 5%, and the cubic symmetry (space group P213) is reduced to orthorhombic (space group P212121) following a translationengleiche group-subgroup relationship of index 3. A fit of a third-order Birch-Murnaghan equation of state to the p-V data results in a bulk modulus B0 = 124(5) GPa with its pressure derivative B0 = 5(1) at V0 = 1134.3(4) Å3 for the low-pressure phase and in B0 = 153(10) GPa with B0 = 3.0(6) at V0 = 1071(3) Å3 for the high-pressure phase. The orthorhombic phase shows an anisotropic axial compression with the a axis (which is the shortest axis) being more compressible (k(a) = 0.0143(4) 1/GPa) than the b and c axes (k(b) = 0.0045(2), k(c) = 0.0058(2) 1/GPa). The experimental results confirm an earlier prediction of the pressureinduced instability of isotypic Ce4[Si4O4N6]O, and also show that the bulk modulus was predicted reasonably well
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