Role of the Madelung energy in hole conductivity in copper oxides: Difference between semiconductors and high-Tcsuperconductors

Abstract

The difference in Madelung site potential, Δ$V_M$, between a hole on a copper site and one on an oxygen site can control the hole’s site preference and ability to delocalize. Among a variety of copper oxide structures, eΔ$V_M$ is shown to vary by ∼3 eV and to clearly separate two classes of compounds: Those with eΔ$V_M$>47 eV are metallic with high $T_c$ and delocalized holes, whereas those with lower Δ$V_M$ are semiconducting because their holes are self-trapped on oxygen.