4 research outputs found
Phonon dispersion and low energy anomaly in CaC
We report measurements of phonon dispersion in CaC using inelastic X-ray
and neutron scattering. We find good overall agreement, particularly in the 50
meV energy region, between experimental data and first-principles
density-functional-theory calculations. However, on the longitudinal dispersion
along the axis of the rhombohedral representation, we find an
unexpected anti-crossing with an additional longitudinal mode, at about 11 meV.
At a comparable energy, we observe also unexpected intensity on the in-plane
direction. These results resolve the previous incorrect assignment of a
longitudinal phonon mode to a transverse mode in the same energy range. By
calculating the electron susceptibility from first principles we show that this
longitudinal excitation is unlikely to be due to a plasmon and consequently can
probably be due to defects or vacancies present in the sample.Comment: Accepted for publication in Physical Review
Superconductivity in Li3Ca2C6 intercalated graphite
In this letter, we report the discovery of superconductivity in Li3Ca2C6.
Several graphite intercalation compounds (GICs) with electron donors, are well
known as superconductors. It is probably not astonishing, since it is generally
admitted that low dimensionality promotes high superconducting transition
temperatures. Superconductivity is lacking in pristine graphite, but after
charging the graphene planes by intercalation, its electronic properties change
considerably and superconducting behaviour can appear. Li3Ca2C6 is a ternary
GIC, for which the intercalated sheets are very thick and poly-layered (five
lithium layers and two calcium ones). It contains a great amount of metal (five
metallic atoms for six carbon ones). Its critical temperature of 11.15 K is
very close to that of CaC6 GIC (11.5 K). Both CaC6 and Li3Ca2C6 GICs possess
currently the highest transition temperatures among all the GICs.Comment: 5 pages, 3 figure
Transition isolant-métal du Rb4C60 (équation d'état et structure électronique)
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF