Electronic Structure of Bi2 Sr2 CaCu2 O8 Single Crystals at the Fermi Level

Abstract

Angle-resolved photoemission has been performed on Bi2 Sr2 CaCu2 O8 single crystals with high energy and angle resolution to study for T>Tc ?he dispersion of the electronic states close to the Fermi level EF. Resonant photoemission has indicated that the states at EF are localized in the Cu-O planes and essentially of O(1) 2p character. The experimental band structure displays only weak dispersions as compared to theoretical results due to important correlation effects. From the Fermi level crossing of the weakly dispersing O2p band along the TX direction the existence of a Fermi surface can be proven. The shape is close to the result of band structure calculations and the unoccupied part becomes visible up to the Brillouin zone boundary in angle-resolved inverse photoemission spectra. Below TC., the opening of the superconductivity gap in the Fermi surface can be observed along TX, yielding a value of 2Δ/kB TC~8. This indicates that Bi2 Sr2 CaCu2 O8 is a strong-coupling superconductor.