Berlin 2005 – scientific programme

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TT: Tiefe Temperaturen

TT 18: Superconductivity - Properties, Electronic Structure, Order Parameter II

TT 18.5: Talk

Monday, March 7, 2005, 11:15–11:30, TU H2053

Density functional theory for superconductors: Applications to MgB₂ and solids under pressure — •Andrea Floris¹, Cesare Franchini², Nektarios Lathiotakis¹, Gianni Profeta³, Sandro Massidda², and E. K. U. Gross¹ — ¹Institut für Theoretische Physik, Freie Universität Berlin, Germany — ²INFM SLACS, Sardinian Laboratory for Computational Materials Science and Dipartimento di Scienze Fisiche, Università degli Studi di Cagliari, Italy — ³C. A. S. T. I. - Istituto Nazionale Fisica della Materia (INFM) and Dipartimento di Fisica, Università degli studi dell’ Aquila, Italy

Understanding and predicting the properties of superconductors is of both fundamental and technological importance. The discovery of superconductivity in MgB₂, of its rather high critical temperature (T_c=39.5K), and the appearance of multiple gaps, has renewed the interest in conventional superconductivity. Here we present several applications of a novel approach to superconductivity that allows one to calculate material-specific properties, such as the gap and the T_c, in a truly ab-initio fashion without using any adjustable parameters. Within this approach, we obtained the T_c and the two gaps of MgB₂ in good agreement with experiment, taking into account the strong anisotropy of both the electron-phonon and the Coulomb interactions. As a further application, we studied the behaviour of T_c in Li and Al as a function of pressure. Despite their common simple metal structure, these materials show different behaviour upon pressure. While Li undergoes several transitions favouring superconductivity, in Al the electron-phonon coupling decreases with pressure leading to a complete suppression of Tc around 8GPa.