The outstanding properties of graphene, a single graphite layer, render it a top candidate for substituting silicon in future electronic devices. The so far exploited synthesis approaches, however, require conditions typically achieved in specialized laboratories and result in graphene sheets whose electronic properties are often altered by interactions with substrate materials. The development of graphene-based technologies requires an economical fabrication method compatible with mass production. Here we demonstrate for the fist time the feasibility of graphene synthesis on commercially available cubic SiC/Si substrates of >300 mm in diameter, which result in graphene flakes electronically decoupled from the substrate. After optimization of the preparation procedure, the proposed synthesis method can represent a further big step toward graphene-based electronic technologies.

PACS numbers:Density waves are inherent to the phase diagrams of materials that exhibit unusual, and sometimes extraordinarily useful properties, such as superconductivity and colossal magnetoresistance [1, 2, 3, 4]. While the pure charge density waves (CDW) are well described by an itinerant approach [5, 6], where electrons are treated as waves propagating through the crystal, the charge-orbital ordering (COO) is usually explained by a local approach [7], where the electrons are treated as localized on the atomic sites. Here we show that in the half-doped manganite La 0.5 Sr 1.5 MnO 4 (LSMO) the electronic susceptibility, calculated from the angle-resolved photoemission spectra (ARPES), exhibits a prominent nesting-driven peak at one quarter of the Brillouin zone diagonal, that is equal to the reciprocal lattice vector of the charge-orbital pattern. Our results demonstrate that the Fermi surface geometry determines the propensity of the system to form a COO state which, in turn, implies the applicability of the itinerant approach also to the COO.

No abstract

Conduction Electron Spin Resonance (CESR) was measured on a thick slab of CaC6 in the normal and superconducting state. Non-linear microwave absorption measurements in the superconducting state describe CaC6 as an anisotropic BCS superconductor. CESR data in the normal state characterize CaC6 as a three-dimensional (3D) metal. The analysis suggests that the scattering of conduction electrons is dominated by impurities and supports the description of superconductivity in the dirty limit. A surprising increase of the CESR intensity below Tc can not be explained by the theoretically predicted change in spin susceptibility. It is interpreted as a vortex enhanced increase of the effective skin depth. The study of the spin dynamics in the superconducting state and the discovery of the vortex enhanced increase of the skin depth poses a challenge to theory to provide a comprehensive description of the observed phenomena.