Ambient pressure superconductivity at 4–5 K in β-(BEDT-TTF)2AuI2

Crystals of β-(BEDT-TTF)₂AuI₂, derived from the sulfur-based organic donor bis(ethylenedithio) tetrathiafulvalene [BEDT-TTF or “ET”] have been synthesized by electrocrystallization and studied by rf penetration depth measurements at ambient pressure and at temperatures down to 0.45 K. The crystals were found to be superconducting at ambient pressure with T_c = 3.93–4.98 K, which represent the highest values of T_c thus far observed at ambient pressure for an organic superconductor. Measurements of the upper critical field anisotropy are reported.     

Evidence of extended fine structures in the Auger spectra: A new approach for surface structural studies

We report for the first time on extended fine structures which we have observed above core-valence-valence Auger transitions on Cu and Co samples. We interpret these oscillating structures as originated from the same interference process which produces extended fine structures observed in the x ray absorption spectra (EXAFS). Using the same EXAFS analysis procedure, we deduce from the extended fine Auger structures (hereafter called EXFAS) the radial atomic distribution F(R) of Cu and Co samples. An excellent agreement is found as compared with results from synchrotron radiation EXAFS.     

Re-examination of the magnetic structure of FeTiO3

The small canting of magnetic spins in the hexagonal antiferromagnet FeTiO₃ is re-examined. In the present study, special attention was paid to multiple scattering effects. Although the previous results was heavily contaminated by the multiple scattering, spins are shown to cant from c-axis with the angle of 1.6 ± 0.1°. The smallness of the canting angle seems to suggest a new mechanism of magnetic interaction.     

Temperature dependence of the fundamental energy gap in GaAs

We show that the temperature dependence of the fundamental gap energy E₀ of GaAs can be theoretically described within the empirical local pseudopotential approach for the band structure. For the calculation we take into account the thermal expansion effect and two contributions of the deformation potential type electron-phonon interaction. These are the Debye-Waller part, which shifts the gap to lower energies with increasing temperature, and the self-energy part, which partly cancels the shift caused by the Debye-Waller part.     

Vibrational modes induced by a pair of impurities

Presence of a polarizable impurity atom in an ionic crystal induces a localized vibrational mode of the lattice. The frequency of the mode is distinct from the propagating modes of the pure crystal. It is shown in this paper that the frequency of the mode depends on the polarizability of the impurity atom and on the distance of separation between two adjacent impurities.     

Dielectric properties of CsBr single crystals-effect of d.c. bias

The dielectric properties of CsBr single crystals, both virgin and γ-irrddiated have been measured as a function of frequency (10³–10⁵Hz), temperature (300–575 K) and d.c. bias (0–350 V cm⁻¹). γ-irradiation produces colour centres in these crystals and consequently an increase in space charge density is observed. D.c. bias has brought in considerable changes in dielectric constant (ϵ') and loss (tanδ) of these crystals particularly at low frequencies and high temperatures. An attempt has been made to understand these data qualitatively through barrier layer formation.     

The multilayer melting transition in methane adsorbed on graphite

High resolution heat capacity measurements of multilayer methane adsorbed on graphite are presented and analyzed. The evidence indicates the presence of two wetting transitions: a first-order dewetting transition at T_w = 90.48 K, and a continuous wetting transition at the triple point, T_t = 90.66 K. This behavior is to be expected in connection with the melting transition in any system where both solid and liquid wet the surface. Heat capacity measurements can provide a valuable diagnostic tool for the wetting behavior of films too thick to be investigated by other means. In the thin film limit, we find that the latent heat of melting vanishes at about 4 layers.     

The effect of dimer mobility on thin film nucleation kinetics

Dimer mobility and dissociation energies of small clusters have been incorporated into a set of rate equations to study the extent of the cluster mobility effect on thin film nucleation kinetics. The numerical analysis results showed that total cluster density and condensation coefficient both increase with increasing dimer dissociation energy and decrease with increasing dimer mobility. By comparison of theoretical calculations with the experimental results of Velfe et al. for Au deposition on NaCl [Thin Solid Films 98 (1982) 15], it is suggested that for this system at 150°C the dimer dissociation energy is low and dimer mobility has little effect on the nucleation kinetics.