Resistivity in Co-doped Ba-122: comparison of thin films and single crystals

The temperature dependence of the resistivity of epitaxial Ba(Fe_(1-x)Co_x)2As2 thin films (with nominal doping x = 0.08, 0.10 and 0.15) has been analyzed and compared with analogous measurements on single crystals taken from literature. The rho(T) of thin films looks different from that of single crystals, even when the cobalt content is the same. All rho(T) curves can be fitted by considering an effective two-band model (with holes and electrons bands) in which the electrons are more strongly coupled with the bosons (spin fluctuations) than holes, while the effect of impurities is mainly concentrated in the hole band. Within this model the mediating boson has the same characteristic energy in single crystals and thin films, but the shape of the transport spectral function at low energy has to be very different, leading to a "hardening" of the electron-boson spectral function in thin films, associated with the strain induced by the substrate.Comment: 13 pages, 4 figure

Linking root traits to copper exclusion mechanisms in Silene paradoxa L. (Caryophyllaceae)

Copper is one of the most important pollutants in mine- contaminated soils. This study tests the response in a sensitive population vs a tolerant one of the model species Silene paradoxa in order to understand the general mechanisms of tolerance at the micromorphological and ultrastructural level. Two populations of Silene paradoxa were grown in hydroponics and exposed to different CuSO4 treatments. The roots were investigated with light, fluorescence and transmission electron microscope. Callose and lignin were spectrophotometrically determined. The tolerant population constitutively possessed a higher amount of mucilage and was able to reduce the length of the zone between the apex and the first lignified tracheids. Callose production decreased. It did not show remarkable copper-induced ultrastructural modifications, apart from the presence of precipitates in the tangential walls. The sensitive population showed huge nucleoli with a spongy periphery in the central cylinder together with the presence of electrondense granules in the mitochondria. Plastids were rarely observed and generally very electrondense and elongated. In the copper tolerant population of S. paradoxa some of the root traits concurring to generate metal-excluding roots were suggested to be mucilage and lignin production and the reduction of the subapical root zone