Jean-Paul Pouget

Bio: Jean-Paul Pouget is an academic researcher from Université Paris-Saclay. The author has contributed to research in topics: Charge density wave & Phase transition. The author has an hindex of 43, co-authored 299 publications receiving 8478 citations. Previous affiliations of Jean-Paul Pouget include Centre national de la recherche scientifique & Brookhaven National Laboratory.

Electron Localization Induced by Uniaxial Stress in Pure V O 2

Abstract: NMR and EPR measurements in V${\mathrm{O}}_{2}$ under uniaxial stress in the ${[110]}_{R}$ direction lead to a phase diagram entirely similar to that obtained in ${\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{2}$ alloys. Two intermediate phases ${M}_{2}$ and $T$ are observed, and, as established for ${\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{2}$, correspond to linear Heisenberg chains of spin \textonehalf{} (${M}_{2}$ phase) on one V sublattice. These chains undergo a progressive dimerization in the $T$ phase as the temperature is lowered.

Charge transport of the mesoscopic metallic state in partially crystalline polyanilines

Abstract: Charge transport properties, including temperature-dependent dc conductivity, thermoelectric power, electron paramagnetic resonance, microwave frequency dielectric constant and conductivity, and electric-field-dependent conductance of partially crystalline (``physically'' cross-linked) HCl-doped polyaniline correlated with x-ray structure studies, demonstrate that charge delocalization in physically cross-linked polyaniline systems is structurally controlled. Further, we observe a positive dielectric constant at room temperature which increases (to values $g~{10}^{4})$ with increasing percent crystallinity, the size of crystalline regions, and polymer chain alignment in the disordered regions, supporting the establishment of mesoscopic metallic regions. We propose an inhomogeneous disorder model for this system in which ordered (crystalline) regions, described by three-dimensional metallic states, are connected through amorphous regions of polymer chains where one-dimensional disorder-induced localization is dominant. We utilize the metallic box, interrupted metallic strands, and Nakhmedov's phonon-induced delocalization models to account for the temperature dependence of charge transport properties of the various partially crystalline polyanilines. Analyses for the sample and temperature-dependent electron paramagnetic resonance linewidth and thermoelectric power are presented.

Dimerization of a linear Heisenberg chain in the insulating phases of V 1-x Cr x O 2

Abstract: The nuclear magnetic resonance (NMR) of ${\mathrm{V}}^{51}$ has been studied in the series of compounds ${\mathrm{V}}_{1\ensuremath{-}x}{\mathrm{Cr}}_{x}{\mathrm{O}}_{2}$ between 100 and 350 K. Three insulating phases are clearly distinguished. In the low-temperature ${M}_{1}$ phase only one V site is seen with a positive Knight shift and electric-field gradient identical to the insulating phase of pure V${\mathrm{O}}_{2}$. At temperatures just below the metal-insulator transition a second phase ${M}_{2}$ is stable in which two sites are resolved. One site has a small positive Knight-shift characteristic of a paired ${\mathrm{V}}^{4+}$ site while the other has a negative Knight shift showing a localized ${\mathrm{V}}^{4+}$ site. These two sites are identified as the V atoms on the paired chains and the equispaced chains in $\frac{C2}{m}$ structure of Marezio et al. At intermediate temperatures a transitional phase $T$ is stable in which two sites can be resolved by their electric-field gradients. The two sites are progressively differentiated by increasing temperature and Cr concentration and are interpreted as arising from two sets of inequivalent paired chains, one of which is depairing with increasing temperature and Cr concentration. These results are inconsistent with the monoclinic symmetry and a disordered bond model proposed previously for the transitional phase. Triclinic splittings were observed recently by Villeneuve et al. and additional crystallographic evidence supporting this result is presented. The magnetic properties are interpreted as a set of noninteracting linear Heisenberg chains and the ${M}_{2}\ensuremath{-}T$ transition as a dimerization of the linear Heisenberg chain. The results demonstrate a breakdown of the band model in the insulating phases.

X-Ray Diffraction

Abstract: Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.