Research | Collaborazioni Scientifiche | Seminari e Convegni

Superconductivity in layered BiS2-based compounds was discovered in 2012 and there are experimental indications that electron-phonon coupling is weak, pointing to an unconventional pairing mechanism, but the origin and nature of the superconductivity is not yet clear, with many different proposals still being investigated. Electron correlationsare generally believed to be moderate in the Bi-based compounds. We focus on the normal state properties of Bi-based superconductors and analize the effect of electron correlat ions: having started with the spectral properties, and the topology of the Fermi surface. Through an analytical treatment for a minimal model consisting of two correlated effective bands proposed to describe bismuth sulphides, we determined the temperature-dependent electron Green`s functions, from which we obtained the spectral density function, improving the description of ARPES results by including moderate electron correlations. We studied the dependence on doping and temperature, predicting also the k-dependence of the spectral density. We described the Fermi-surface topological transition at a critical doping value in bismuth sulphides. To complete our study of the normal state properties, more recently (in yet unpublished results) we determined the normal-state electrical conductivity (resistivity) and the Hall coefficient, using the Kubo formalism, comparing our results with experimental data available for bismuthates, again obtaining improved descriptions of the experimental transport data with the inclusion of moderate electron correlations. We also evaluated thermal transport properties: the Seebeck factor as a function of doping and temperature, electronic thermal conductivity, the power factor, and the ZT figure of merit.