Mott transition for picosecond all-optical nor gate in CdSe

Using picosecond time resolved spectroscopy, we study the extinction kinetics of the optical transmission of CdSe platelets induced by strong optical pumping. We investigate particularly the all-optical gate capabilities (resulting from the bandgap shrinkage due to the Mott transition) for laser beams the wavelength of which ranges from 676 to 678 nm. The electron-hole plasma density necessary to enable the optical switching is determined (ϱ ∼ 2 × 10¹⁷cm⁻³ at 20K). The switch-off time (i.e. the transparency recovery time) is also studied at different wavelengths by picosecond spectroscopy.     

Incommensurate CDW in Rb0.3MoO3: 87Rb NMR

The ⁸⁷Rb NMR measurement was carried out in a single-crystal Rb_0.3MoO₃. Below 180 K the NMR line well characterized the existence of incommensurate CDW. The absence of lock-in transition was confirmed from the temperature dependence of line shape. The CDW held the incommensurate phase even at 77 K, in spite of the nearly commensurate value of CDW wave vector observed in the neutron diffraction experiment. The CDW amplitude obtained from NMR was consistent with the BCS curve.     

Lattice dynamics and superionic properties of Cd1−xPbxF2 crystals

Reflectivity in the infrared range, Raman scattering and ionic transport properties in Cd_1−xPb_xF₂ crystals have been investigated. A “one-mode” behaviour of these crystals has been found. The role of the PbF₂ cation sub-lattice in the anion disordering process has been discussed. A correlation has been found between the ionic transport properties and the fluorine-cation interaction coefficient for Cd_1−xPb_xF₂ crystals.     

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.     

Conductivity and thermoelectric power of NbS3+δ

The conductivity and thermoelectric power of samples from two different NbS_3+δ compounds have been measured in wide ranges of temperatures below 430K. The compound with the larger excess of sulfur was found to be stable upon treatement with CS₂ and heat treatment. Its conductivity exhibits two anomalies, a sharp one around 360K and a broad one around 150K. The results obtained for these compounds are compared with the results reported in the literature for other NbS_x compounds and for TaS₃.     

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.     

Influence of the ordering of carbon vacancies on the electronic properties of TiC0.625

Annealing of f.c.c. TiC_0.625 for 10 days between 780 and 750°C leads to a trigonal superstructure by ordering of carbon vacancies. Long-range ordering decreases slightly the residual electrical resistivity ϱ(1.6 K) and the electronic specific heat and increases the temperature coefficient of the resistivity dϱ/dT between 100 and 300 K. A minimum in ϱ(T), more apparent in the disordered samples (around 65 K) is attributed to the scattering of electrons by the strong atomic disorder.     

Attenuation of ultrasound in p-wave superconductors

The theory of ultrasound attenuation in impure BCS superconductors is extended to unitary p-wave states. For the ABM state, but not for the polar state, a set of parameters can be found such that the theoretical predictions agree reasonably well with the experimental data on UPt₃.     

Mictomagnetic behaviour in MnAlC(Ni) alloys

The as cast, thermally treated and hot extruded Mn_1.058Al_0.909C_0.022Ni_0.011 samples were investigated by X-rays, neutron diffraction and magnetic measurements. The hot extruded magnets produced by Matsushita Electric Ind. Co., having (BH)_max = 5 MGOe, show a mictomagnetic-type behaviour.