Superconductivity of bulk CaC6

We have obtained bulk samples of the graphite intercalation compound, CaC6, by a novel method of synthesis from highly oriented pyrolytic graphite. The crystal structure has been completely determined showing that it is the only member of the MC6, metal-graphite compounds that has rhombohedral symmetry. We have clearly shown the occurrence of superconductivity in the bulk sample at 11.5 K, using magnetization measurements.     

First Spectra from a New, Wide Band, Hybrid Digital Correlator Spectrometer for the First-HIFI Instrument

We have designed and built a new, wide band, modulable resolution spectrometer, in view of full astronomical qualifying tests, and to prepare future models for the FIRST satellite's heterodyne instrument. Our spectrometer, a hybrid digital Autocorrelator, offers flexibility in terms of bandwidth (from 170MHz to 680MHz) and resolution (from 700kHz to 3MHz). This spectrometer required the development of a dedicated analog filter bank, homemade samplers, and the design of full custom GaAs integrated circuits.Laboratory tests have shown excellent agreement with expected performances and observations performed with the IRAM 30-m radiotelescope have qualified its capabilities. Despite the relatively limited number of channels of our current prototype compared to others spectrometers, the main advantages are its stability (inherent to digital technique), and its spectral versatility.Recent microelectronics advances and rad-tolerance of our spectrometer components are used to prepare a new, compact, and low power consumption autocorrelator in view of a flight model for HIFI, the heterodyne instrument on the ESA cornerstone mission FIRST.     

Die Verwendung des elektrischen Stromes als W?rmequelle

Ohne Zusammenfassung     

Superconductivity of the graphite intercalation compounds KHgC8 and RbHgC8

Superconductivity was observed in the graphite intercalation compounds, KHgC₈ and RbHgC₈, using an AC induction technique. The transition temperatures were 1.90K and 1.44K for KHgC₈ and RbHgC₈ respectively. A full Meissner effect was observed for KHgC₈ with a temperature dependant anisotropy in critical field with a value of 25 ± 5 at T_c.     

Optical properties of stages 1 and 2 potassium mercurographitides

We have measured the reflectivity spectra of stages 1 and 2 graphite intercalated with KHg amalgam (KHgC₄ and KHgC₈) from 0.5–6eV, and compared them to the corresponding stages 1 and 2 binary compounds, KC₈ and KC₂₄. Plasma edges for the ternaries appear at about the same energies as in the binaries, but differences are observed in the reflectivity values at the minima. Kramers-Kroenig analysis yields thresholds for the onset of interband transitions at 1.3eV and 1.2eV for KHgC₄ and KHgC₈, compared to 2.7eV and 1.7eV for KC₈ and KC₂₄. The thresholds are explained in terms of interband transitions in the mercurographitides involving the Hg levels. A model for these transitions is presented based on the Mott metal-semiconductor transition in mercury. This model is shown to be consistent with the hypothesis that the mercury layers are negatively charged.