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TT: Tiefe Temperaturen
TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...
TT 18.1: Talk
Tuesday, March 28, 2006, 15:00–15:15, HSZ 02
Three-Dimensional MgB2-Type Superconductivity in Hole-Doped Diamond — •Jens Kortus1, Lilia Boeri2, and Ole K. Andersen2 — 1Theoretische Physik, TU Bergakademie Freiberg, Germany — 2MPI FKF Stuttgart, Germany
We substantiate by numerical and analytical calculations that the recently discovered superconductivity in boron-doped diamond is caused by electron-phonon coupling of the same type as in MgB2, albeit in three dimensions. Using first-principles linear response methods based on density functional theory we obtain the phonon dispersion and the electron-phonon coupling strength as function of hole doping. As revealed by these calculations, holes at the top of the zone-centered, degenerate sigma-bonding valence-band couple strongly to the optical bond-stretching phonon modes. This mechanism shows several very similar aspects to the one which drives the superconductivity in MgB2. However, the increase from two dimensions in MgB2 to three dimensions in diamond reduces the phonon mode softening crucial for the high Tc of 40 K in MgB2. Even if diamond had the same bare coupling constant as MgB2, which could be achieved with higher doping, Tc would be limited to only 25 K. Using the same theoretical methods we also investigate the possibility of superconductivity in the isostructural and isoelectronic semiconductors Si and Ge. Superconductivity above 1 K in Si (Ge) requires hole doping beyond 5% (10%).
L. Boeri, J. Kortus, O.K. Andersen, Phys. Rev. Lett. 93, 237002 (2004)