Shuzo Takano

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.

Studies of Dielectric Properties and Band Parameters of N-Pb1-xSnxTe by Magnetoplasma Waves

From magnetoplasma experiments at 50 GHz for n -Pb 1- x Sn x Te (0≤ x < 0.3), a static dielectric constant e s is determined as a function of x . For x =0, 0.063, 0.091, 0.152 and 0.293, e s is found to be 1410, 1770, 2840, 4610 and 10800 at 1.6 K, respectively. e s seems to depend on band gap as well as on carrier density. It is suggested that free carriers tend to stabilize the lattice instability and that the transition to the ferroelectric phase would be possible at around x =0.2 if the carrier density would be very small. It is further found that the band structure of alloys is essentially the same as that of PbTe at least up to x =0.3.

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...

Anomalous Three-LO-Phonon Assisted Cyclotron Resonance with Spin-Flip Transitions in n-InSb

We have reexamined “photo-induced magnetophonon resonanc” (\(n\hbar\omega_{C}{=}\hbar\omega_{LO}\)) in n-InSb previously observed by a part of our group by measuring its dependence on the photon energy with a tunable CO 2 laser and have proved that this resonance is three-LO-phonon assisted cyclotron resonance. This resonance occurs at the magnetic field of \(\hbar\omega{=}3\hbar\omega_{LO}+E_{n,s}\), - E 0,↓ and appears as minima in the photoresponse. We also examined the amplitudes and the damping constants of this resonance by the method of magnetic derivative of photoresponse. As a result, this resonance were divided into three series with different amplitudes and damping constants.

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.

Resistivity Anomalies in Pb1-xGexTe at Low Temperatures

Electrical measurements of n- and p-Pb 1- x Ge x Te have been made between 4.2 K and 300 K. Below 40 K, resistivity exhibits anomalous behaviours similar to the Kondo effect in a dilute magnetic alloy. The anomaly is strongly correlated with the phase transition temperature. The formation of the pseudo-spins and the effect of their ordering on the resistivity anomaly are discussed.

Power Spectrum Analysis of Quantum Oscillations of the Velocity of Sound in Antimony

By the power spectrum analysis of the quantum oscillations of the sound velocity in antimony, the geometrical factors G of the energy surfaces were studied. For holes it was found that G is ellipsoidal for the light mass directions. The coupling constants of holes with the sound wave were determined from the peak values of the power spectrum as follows: | C x d | 2 =20.0 ±1.0, | C x f | 2 =1.6 ±0.3, | C y d | 2 =5.65 ±0.30, | C y f | 2 =5.95 ±0.40 and | C z d | 2 =0.55 ±0.05 eV 2 . It was also found that for electrons G differs from the ellipsoid. The coupling constants were determined under the assumption that the densities of states of electrons and holes at zero magnetic field are given by the ellipsoidal models. The results are: | C x a | 2 =18.2 ±3.6, | C x b | 2 =8.66 ±1.7, | C y a | 2 =22.6 ±5.0, | C y b | 2 =2.78 ±0.55 and | C z a | 2 =0.475 ±0.043 eV 2 .

Quantum Oscillations of Velocity of Sound in p-Pb1-xGexTe in Rhombohedral Phase

Quantum oscillations of shear acoustic wave were observed in p -Pb 1- x Ge x Te ( x =0.014) at liq. He temreratures. Three kinds of different branches of the frequencies were resolved by the Fourier analyses of the oscillations. By comparing with the theoretical model of the energy surfaces by Takaoka and Murase, these oscillations were identified as arising from the triplet up-, the triplet down- and the singlet down-state energy surfaces. The singlet up- energy surface is too small to be observed. From the ratios of the observed frequencies for magnetic field parallel to the major axis of the energy surfaces, we estimated Δ E v =0.006 eV and \(\varXi u{=}0.06\) eV where Δ E v is the downward shift of the valence band edge at L-point relative to that at T-point, \(\varXi\) is the optical deformation potential constant and u is the internal displacement of the sublattices.

Renormalization of Velocity of Sound in Bismuth in Magnetic Field

Quantum oscillations of 20 MHz longitudinal velocity of sound are measured at liquid helium temperatures in magnetic fields up to 23 kOe for single crystals of pure and tellurium doped bismuth. It is found that for sound wave propagating parallel to the bisectrix axis, non-principal electrons do not contribute to the oscillations in pure bismuth, but, in doped bismuth in which no hole is present, all groups of electrons contribute to the oscillations. It is shown that this experimental fact indicates the importance of the effect of the screening in the process of the renormalization of the phonon frequency in a semimetal.