Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 18: Superconductivity: Borides, Borocarbides, Carbides, ...

TT 18.1: Vortrag

Dienstag, 28. März 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 T_c 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)