RESUMEN
By means of a specific heat (C) and electrical resistivity ([Formula: see text]) study, we give evidence of a pronounced Fermi liquid (FL) behavior with sizable mass renormalization, [Formula: see text], up to unusually high temperatures â¼70 K in the layered system (Cu2/3V1/3)V2S4. At low temperature, a marked upturn of both C and [Formula: see text] is suppressed by magnetic field, which suggests a picture of Kondo coupling between conduction electrons in the VS2 layers and impurity spins of the V3+ ions located between layers. This picture opens the possibility of controlling electronic correlations and the FL to non-FL crossover in simple layered materials. For instance, we envisage that the coupling between layers provided by the impurity spins may realize a two-channel Kondo state.
RESUMEN
We measured the temperature dependent resistivity, varrho(T), of the intercalated graphite superconductor CaC6 as a function of pressure up to 16 GPa. We found a large linear increase of critical temperature, Tc, from the ambient pressure value 11.5 K up to 15.1 K, the largest value for intercalated graphite, at 7.5 GPa. At approximately 8 GPa, a jump of varrho and a sudden drop of Tc down to approximately 5 K indicates the occurrence of a phase transition. Our data analysis suggests that a pressure-induced phonon softening related to an in-plane Ca phonon mode is responsible for the Tc increase and that higher pressures greater, similar8 GPa lead to a structural transition into a new phase with a low Tc less, similar3 K.
RESUMEN
We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with Delta0=1.6+/-0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane xiab approximately 33 nm.
RESUMEN
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.
RESUMEN
In order to obtain reliable Compton spectra using high-energy photons, the scattered beam must be free of parasitic photons, because of the weakness of the double-differential inelastic cross section. The purpose of the device presented in this paper is to remove photons scattered by air, the sample holder or any other stopper. It has been tested on ESRF beamline 2, which is devoted to materials science.