ELECTRONIC-STRUCTURE OF ORGANIC SUPERCONDUCTORS KAPPA-(ET)(2)CU[N(CN)(2)]BR, KAPPA-(ET)(2)CU(NCS)(2), AND BETA-(ET)(2)I-3 STUDIED BY PHOTOELECTRON-SPECTROSCOPY

Photoemission studies were carried out on three organic superconductors: -(ET)2Cu[N(CN)2]Br, -(ET)2Cu(NCS)2, and -(ET)2I3. In all three compounds, we observe a valence band that extends from the Fermi level to approximately 22 eV below, showing many distinguishable features. A metallic Fermi edge is not observed in any of the three compounds. The orbital characteristics of some spectral features are deduced through variations in the excitation photon energy and observations of the relative intensity variations. For -(ET)2Cu[N(CN)2]Br and -(ET)2I3, comparisons were made between the measured spectra and the densities of states calculated by use of first-principles self-consistent methods. Some core-level spectra are presented. © 1995 The American Physical Society.