New High Temperature Diboride Superconductors: AgB2 and AuB2

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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 λis much larger in AgB2 and AuB2 than in MgB2. Estimated transition temperatures for AgB2 and AuB2 are Tc = 59 K and 72 K, respectively. These are about 2 3 times higher than the estimated Tc = 27 K in MgB2 and almost comparable to those in cuprate superconductors.