Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 36: Superconductivity: Properties, Electronic Structure, Order Parameter
TT 36.3: Vortrag
Freitag, 29. Februar 2008, 10:45–11:00, H 0104
Superconducting properties of CaC6 — •Antonio Sanna1,2, Gianni Profeta3, Andrea Floris2, Andrea Marini4, Eberhard K.U. Gross2, and Sandro Massidda1 — 1Università degli studi di Cagliari, Italy. — 2Freie Universität Berlin, Germany. — 3Università degli studi dell’Aquila, Italy. — 4University of Rome Tor Vergata, Italy.
We present first-principles calculations of the superconducting properties of CaC6[1], obtained within the density functional theory of superconductivity (SCDFT). We find an anisotropic gap which is larger on the Fermi surface sheet with interlayer character. In contrast to MgB2 the intraband anisotropy is large and the gaps on the three Fermi surface sheets overlap. The resulting critical temperature of 9.5 K is in good agreement with the experimental value of 11.5 K.
We show that anisotropy improves the agreement between calculated and experimental specific heat and is consistent with tunnelling experiments. A direct evidence of the gap anisotropy in CaC6 has been recently observed in directional point contact measurements[2].
We also investigate the system under pressure in order to analyse the increase of the superconducting critical temperature reported experimentally[3] but not reproduced in the McMillan approach. Within our SCDFT implementation we intend to improve the theoretical description with respect to previous studies introducing an ab-initio and pressure-dependent Coulomb interaction.
[1] A. Sanna et al., Phys. Rev. B 75, 020511 (2007).
[2] R. Gonnelli et al., arXiv 0708.0921.
[3] A. Gauzzi et al., Phys. Rev. Lett. 98, 067002 (2007).