Hajimu Kawamura

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.

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.

Interaction of the TO-phonon with the Acoustic Phonons near the Phase Transition Temperature in Pb1-xGexTe

The phase transition in Pb 1- x Ge x Te with x =0.03 ∼0.1 was studied by Raman scattering and ultrasonic velocity measurements. Below T c the frequency of the A 1 -mode is 1.99 ×10 23 ( T c - T ) rad 2 /sec 2 and the E -mode 5.32 ×10 23 ( T c - T ) rad 2 /sec 2 for x =0.05. The ultrasonic velocity shows a step-like behaviors at T c . Just above T c the normal elastic moduli are C 11 =11.0 ×10 11 , C 12 =0.02 ×10 11 and C 44 =1.35 ×10 11 in dyn/cm 2 . The steps are Δ C 11 =1.52 ×10 11 , Δ C 12 =-0.20 ×10 11 and Δ C 44 =0.26 ×10 11 in dyn/cm 2 . The parameters of the free energy expansion were calculated by using the above results together with the data of the shear strain. The order parameter, the spontaneous strain and the TO-phonon frequency above T c which were estimated from thus obtained parameters are consistent with the results experimentally obtained satisfactorily.

Observation of soft TO-phonon in SnTe by Raman scattering

Abstract The soft TO-phonon in SnTe ( p = 1.1 × 10 20 cm −3 ) has been observed by Raman scattering below the phase transition temperature ( T c = 105 K ). The temperature dependence of the phonon frequency is given by ω TO 2 = γ ( T c − T ) cm −2 . Several temperature independent peaks and a center peak which is temperature dependent are also observed.

The Quantum Variation of Fermi Energy in Bismuth under High Magnetic Fields

Alfven wave transmission through bismuth single crystals is measured using 50 Gc microwave interferometer under pulsed magnetic field up to 200 kG at liquid helium temperatures. It is found that the mass densities change remarkably with magnetic field for all cases studied. These changes are ascribed to the quantum variation of Fermi energy at high magnetic field. The shifts of Fermi energy are determined as a function of magnetic field assuming the nonparabolic band for holes. From the analysis based on the Baraffs theory, it is found that the lowest Landau levels of light electrons go down linearly with magnetic field instead of the parabolic change expected from the modified two band model. It is also found that the lattice dielectric constant has an anisotropy. If \(\varepsilon_{\bot}{\doteqdot}100\) is adopted according to Boyle and Brailsford, we obtain \(\varepsilon_{//}{\doteqdot}60\) in the present experiments, where e // and e ⊥ are the dielectric constants for waves polarized along and perpend...

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.

Line Shape of LO-Phonon Assisted Cyclotron Resonance in n-InSb

The line shape of the LO-phonon assisted cyclotron resonance (PACR) is calculated on the basis of the theory of Enck et al. Measured values of the resonance magnetic field, full width and peak height of PACR in n-InSb are compared with theory. The results show that the strong coupling between Landau levels through LO-phonon (polaron pinning) gives rise to the anomalous line broadening and peak shift.

Photo-induced magnetophonon resonance in n-InSb at 4.2°K

Abstract Spin-flip and two-phonon as well as normal magnetophonon resonance are observed in CO2-laser-irradiated photoconductivity in n-InSb at 4.2°K. The effects are attributed to the resonant cooling of photo-excited electrons due to optical phonon emission.

On the Anomalous Angular Variation of the Spin Splitting Factor of Bismuth

The two band model is a good approximation for the energy band structure of the electrons in bismuth, and consequently the spin splitting factor of electron becomes nearly one. However, detailed studies on giant quantum attenuation of ultrasonic waves show that the spin splitting factor has an anomalous angular dependence. This behavior is explained in terms of the quantum variation of the Fermi energy caused by a strong magnetic field.