  Based on electronic structure calculations, we have found that noble metal
diborides, AgB2 and AuB2, are potential candidates for conventional BCS-type
high temperature superconductors. B 2p density of states dominates at the Fermi
level in comparison with Ag 4d and Au 5d states. Furthermore, the
electron-phonon coupling constant \lambda is much larger in AgB2 and AuB2 than
in MgB2. Estimated transition temperatures for AgB2 and AuB2 are T_c = 59 K and
72 K, respectively. These are about 2 ~ 3 times higher than the estimated T_c =
27 K in MgB2 and almost comparable to those in cuprate superconductors.
