• Nabonita Deb Chowdhury

      Articles written in Pramana – Journal of Physics

    • Nonlinear lattice dynamical theory for valence transition in rare earth compounds

      Nabonita Deb Chowdhury Sankar P Sanyal

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      A nonlinear lattice dynamical theory is proposed to explain the mode softening in intermediate valence compound Sm0.75 Y0.25 S. In this theory we consider the breathing motion of the electron shells of Sm-ion to be nonlinear, and depend on temperature, resulting in strong electron-ion coupling. We calculate the salient features of the nonlinear breathing potential, which resembles theφ4 potential for second order ferro-electric transitions. We also calculate the temperature dependence of LO(L) frequency for this compound, showing that at transition temperature (about 200 K) this mode freezes.

    • Anharmonic oxygen vibration and mode softening in Tl2Ba2Ca2Cu3O10 superconductor

      Nabonita Deb Chowdhury Sankar P Sanyal

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      The softening of the IR active 300 cm−1 phonon mode in Tl-2223 superconductor, aroundTc has been explained by considering a sixth order polarization potential at the off-center oxygen ion site in the Tl-O plane, and by using a nonlinear lattice dynamical theory. The present theory explains, more or less satisfactorily, the unusual temperature dependence of oxygen ion vibration and frequency shifts at higher temperature. The existence of strong nonlinear electron-phonon interaction atTc has been emphasized.

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