Evidence for non-metallic nature of the BiO plane in Bi2CaSr2Cu2O8 from scanning tunnelling spectroscopy

Abstract

THE existence of Fermi-liquid electronic states in the high-Tc superconductor Bi2CaSr2Cu2O8 has been experimentally established by angle-resolved photoemission spectroscopy1. The nature of these states has been studied by various high-energy spectroscopies1–5, all of which indicate that the electronic states at the Fermi energy reside mainly in the oxygen 2p orbital with in-plane symmetry. The question remains as to which plane in the crystal, BiO or CuO2, provides the O 2p orbitals at the Fermi energy. This point is important in modelling the high- Tc mechanism, because if the Fermi-liquid states were supplied by the BiO plane, which is not present in the copper oxide high-Tc superconductors, mechanisms based on the Fermi-liquid states would lose their direct experimental basis. Here we present results from scanning tunnelling spectroscopy (STS), combined with photoemission (PES) and inverse photoemission (IPES) spectroscopies, which show that the BiO planes are non-metallic and the O 2p orbitals in the CuO2 planes form the Fermi-liquid states.