Dresden 2006 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 7: Superconductivity & Solids At Low Temperature - Poster Session
TT 7.6: Poster
Montag, 27. März 2006, 14:00–17:45, P1
CaSi2, the “antibonding sister” of MgB2 — •Claire Loison and Helge Rosner — Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Str. 40, 01187 Dresden, Germany
After the suprising superconductivity of MgB2 at 40 K, the superconductivity of other solids with the layered AlB2-type has been discovered recently: CaSi2, CaAlSi, SrAlSi (Tc ∼ 14 K, 8 K and 4 K respectively). At the same time, similar layered compounds, like the intercalated graphites YbC6 and CaC6 are discovered to superconduct at temperatures substancially higher than previously known for other intercalated graphites (6.5 K and 11 K respectively). Here, we study the electronic structure and the electron-phonon coupling of the superconducting phase of CaSi2 using density functional theory, and compare it to MgB2. The crystal structure of superconducting CaSi2 is also of the AlB2-type, with a slight buckling in the silicon planes. Superconductivity mechanism is similar in MgB2 and CaSi2, except that in CaSi2 the antibonding σ*-bands of the silicon layers are main contributor to the electron-phonon coupling, whereas in CaSi2, it is the bonding 2p-σ-bands of boron. We investigate the influence of the buckling, which can be controled experimentally by the pressure, on the electron-phonon coupling. Finally, we discuss the possibility to find other superconductors in the familly of metal disilicides ASi2 with A = Ba Ca, Lu, Sc, Yb.