title: Three-dimensional MgB2-type superconductivity in hole-doped diamond.
abstract: We substantiate by numerical and analytical calculations that the recently discovered superconductivity below 4 K in 3% boron-doped diamond is caused by electron-phonon coupling of the same type as in MgB2, albeit in three dimensions. Holes at the top of the zone-centered, degenerate sigma-bonding valence-band couple strongly to the optical bond-stretching modes. The increase from two to three dimensions reduces the mode softening crucial for T(c) reaching 40 K in MgB2. Even if diamond had the same bare coupling constant as MgB2, which could be achieved with 10% doping, T(c) would be only 25 K. Superconductivity above 1 K in Si (Ge) requires hole doping beyond 5% (10%).
authors.affiliation: INFM SMC and Dipartimento di Fisica, Università la Sapienza, Piazzale Aldo Moro 2, 00185 Rome, Italy.
authors.forename: Lilia
authors.initials: L
authors.lastname: Boeri
authors.forename: Jens
authors.initials: J
authors.lastname: Kortus
authors.forename: O K
authors.initials: OK
authors.lastname: Andersen