W.R. Datars

Two-phonon absorption in InP and GaP☆

Abstract Far-infrared absorption in crystals of GaP and InP was investigated using a high-resolution Fourier-transform spectrometer. The two-phonon absorption was found to be very similar in these two materials. Van Hove singularities on the GaP spectrum were identified with the aid of calculated two-phonon sum and overtone density-of-states curves. The analysis of the InP spectrum was based on its homology to GaP. Many of the prominent features of the absorption spectra are assigned to pairs of phonons on the hexagonal face of the Brillouin zone while phonon pairs at Γ, X and L generally contribute only minor features to the spectra.

Electrical conductivity of linear chain mercury compounds

Abstract The electrical conductivity of the compounds Hg2,86AsF6 and Hg2.91SbF6 containing linear cationic chains of mercury atoms with a mercury-mercury distance that is incommensurate with the lattice has been measured from 4.2 to 300K. It is shown that they have anisotropic metallic conductivity that increases markedly with decreasing temperature.

Anisotropic optical reflectance of Hg2.91SbF6

Abstract The optical reflectivity of Hg2.91SbF6 single crystals was measured in the visible and near infrared regions with light polarized parallel and perpendicular to the mercury chains. The results for the parallel polarization were fitted to a dielectric model consisting of a Drude term and two Lorentzian functions describing peaks in the visible. The spectrum for the perpendicular polarization had a reflectance peak in the visible and a small, relatively constant reflectance in the infrared. The results show that Hg2.91SbF6 is an anisotropic metallic conductor.

A pressure induced anomaly in the Fermi surface of ReO3

Abstract De Haas-van Alphen frequencies of ReO 3 have been measured as a function of pressure up to 5 kbar with the magnetic field along [111] and [001] crystallographic directions. The variation of the frequencies with pressure is linear at low pressure and for the α frequency follows free electron scaling predictions. Above 3 kbar, all cross-sectional areas increase much faster with pressure. The area compressibilities are one order of magnitude higher than the low-pressure area compressibilities. This anomalous increase may be attributed to an increase in covalent bonding or a rotation of the oxygen atoms at high pressure.

Changes with temperature of the cylotron mass, and relaxation time of electrons in mercury

Abstract Measurements of the temperature dependences of the cyclotron mass and relaxation time of electrons in single crystal mercury have been made using Azbel-Kaner cyclotron resonance at 34.28 GHz. Between 1.15 and 2.1 °K, ωτ varied from 20.1 to 10.8 and the temperature dependent part, τel-ph, of the relaxation time, τ, varied as T−4.8. For the same temperature range, the cyclotron effective mass increased (1.2 ± 0.3) per cent. These changes with temperature of τ and the cyclotron mass are attributed to, and yield new information about, the strong electron-phonon interaction in mercury.

Azbel'-Kaner cyclotron resonance in mercury

Abstract Azbel-Kaner cyclotron resonance has been observed from the first zone Fermi surface in single crystal mercury. The orientation of the sample was such that two of the three 〈100〉 directions were parallel to the sample surface and cyclotron effective mass data have been correlated with open orbits along these directions. Complementary transverse magnetoresistance data are also presented.

Temperature dependence of the induced torque of potassium

Abstract Sharp peaks observed in the induced torque of potassium as a function of magnetic field direction above about 4 T are temperature dependent in the range 1.1–1.9 K that was investigated. The amplitude and magnetic field direction of some of the peaks change with temperature. Induced torque amplitude at a fixed field direction and magnetic field above 4 T changes non-monotonically with temperature. The high-field peaks are independent of the presence of a four-fold torque which depends on sample conditions.

Search for linear magnetoresistance in aluminum

Abstract The induced torque from high-purity aluminum for magnetic field rotation in a (100) plane exhibits little high-field linear magnetoresistance except for a narrow angular region (±3°) around 〈100〉 directions. The dimensionless slope of the high-field magnetoresistance determined from the induced torque is up to 25 times smaller than that determined previously by four-probe measurements. This suggests that the generally observed high-field linear magnetoresistance is not an intrinsic effect. An increase in the induced torque at 〈100〉 suggests the existence of open or extended orbits at high fields for this magnetic field direction.

Electrical transport in superconducting BiPbSrCaCuO

Abstract Measurements of the magnetic field and temperature dependent electrical resistance and thermoelectric power of a lead-doped polycrystalline sample of BiPbSrCaCuO are reported. According to the d.c. susceptibility data, the sample shows a major Meissner effect at 110 K with an additional feature at 80 K which indicates the presence of the second phase. Magnetoresistance is muck less sensitive to the fraction of the second phase than are the thermopower measurements that clearly resolve a shoulder-like structure at 80 K. The application of a magnetic field results in a positive contribution to the thermopower, S(B, T), below the Tc of the zero-field superconducting phase transition. Based on an analysis of the S(B, T) in terms of the transport entropy of the vortex motion we find that the data for lead-free (Tc = 85K) and lead-doped (Tc = 110K) BiSrCaCuO compounds provide a reasonable estimate of the principal quantum unit h 2m of the particle flux.

Magneto-electrical measurements of superconducting BiSrCaCuO

Abstract Measurements of the electrical resistance, Hall effect and magnetization have been made in fields between zero and 1.5 T on a polycrystalline sample of BiSrCaCuO. Above 120 K the resistance is linear with temperature and has no dependence on magnetic field. A superconducting transition is observable at 85 K and shows a depression of approximately 1 K T −1 in applied fields. The Hall coefficient R H increases as the temperature is increased through T c . There is a corresponding decrease in the Hall mobility to a constant value of 3.5 × 10 −8 G −1 above 120 K. The measurements above 120 K are consistent with a conductivity that is limited by a metallic-like phonon scattering, with a carrier mean free path which is much smaller than the average crystallite dimension.