S. Katayama

Dielectric constant and soft mode of Pb1−xSnxTe

Abstract We try to explain the large dielectric constant of Pb 1- x Sn x Te pseudobinary alloy system in terms of the softening of TO-phonon mode due to electron—phonon coupling. The order of magnitude estimation shows that the interband optical deformation potential of several electron volts is sufficient to explain the softening of phonon.

Role of local displacement of Ge ions on structural instability in Pb1−xGexTe

Abstract This note presents a simple theoretical model to explain curious alloy effects on the occurrence of lattice instability in Pb 1− x Ge x Te. Our model is based on the assumption that the substitutional Ge 2+ ion is unstable to the displacement from the regular cation site due to its small ionic radius compared with that of the Pb 2+ ion. The observed strong dependence of T c on the composition x as well as the temperature variation of 1 ϵ s can be well explained in terms of coupling between the local dipoles produced by the off-site Ge ions and the optical phonons of PbTe on the basis of a cooperative Jahn-Teller-like description.

Carrier density dependence of soft TO-phonon in SnTe by Raman scattering

Abstract The frequency of soft TO-phonon in SnTe was observed by Raman scattering below the transition temperature, for the specimens of various carrier concentrations. The result was analyzed in terms of the interband electron to TO-phonon interaction.

Dielectric constant and soft mode of Pb1-xSnxTe by magnetoplasma reflection

Abstract The static lattice dielectric constant and TO-phonon frequency were measured by means of magnetoplasma reflections of 6 mm and 337 μ waves at 1.6 K for n -Pb 1- x Sn x Te with various tin compositions and carrier densities. The experimental results was interpreted in terms of the softening of TO-phonon induced by the interband electron-phonon coupling.

Structural instabilities and transverse effective charges in IV–VI compounds

Abstract Transverse effective charges for some IV–VI, III–V and II–VI compounds are investigated on the basis of the interband electron-phonon coupling with the use of the Penn model for electron energy bands. The results show that the large transverse effective charges of IV–VI compounds are related with strong electron-phonon interaction as well as with the softening of TO phonon in IV–VI compounds.

Anomalous resistivity in structural phase transition of IV–VI

Abstract The contribution of a carrier-soft optical phonon interaction to the electrical resistivity of IV–VI compounds is discussed. The calculated resistivity based on a soft mode theory shows a large increase near the transition temperature Tc. It is foound that the observed increase of resistivity of p-SnTe is reproduced by the carrier-soft TO phonon interaction.

Phonon and electrical resistivity anomalies at the displacive phase transition in Pb 1−XSnXTe and Pb 1−XGeXTe

We present low temperature electrical transport measurements on Pb1−x (Sn,Ge)xTe under hydrostatic pressure. We emphasize the differences between the anomalous increment in resistivity in the vicinity of the structural phase transition of PbSnTe and PbGeTe. We propose explanations for the anomalous resistivity increment and the pressure shift of the phase transition temperature.

Raman Scattering Due to Coupled Phonon-Damped Plasmon Mode in N-GaAs

The coupled mode of phonon with plasmon in the region of Landau damping has been observed for the first time in Raman spectra. The back-scattering from (100) face with Ar-ion laser lines has enabled us to investigate the dispersion of this coupled mode for the heavily doped n-GaAs specimens. The mode appeared as a broad band with the width of more than ten kaisere overlapping with the sharp TO (almost forbidden) line. The dispersion relation of the coupled mode was calculated, being taken into account of the nonlocal effect due to the coupling with the single particle excitations.