Electronic Structure of the Organic Conductorsκ-ET2Cu(SCN)2andκ-ET2Cu[N(CN)2]Br Studied Using Soft X-ray Absorption and Soft X-ray Emission☆

Abstract The problem of resolving molecular components of the electronic structure of complex, organic solids with respect to their chemical and orbital character has been approached using core-level photon spectroscopies. Specifically, the bulk C 2 p occupied and unoccupied partial densities of states (PDOS) of the organic superconductors κ -ET 2 Cu(SCN) 2 and κ -ET 2 Cu[N(CN) 2 ]Br were measured using a combination of high-resolution soft X-ray absorption (SXA) and soft X-ray emission (SXE). The PDOS was also calculated using a tight binding model, and the measured spectra compared directly to that predicted by the calculations. The emission and absorption spectra from both materials were found to be quite similar, reflecting mostly contributions from the common conductive ET layers. The presence of two nonequivalent carbon sites of the ET molecule was identified in the SXA spectra. Contributions from the π and σ states were identified in the emission spectra. The occupied C 2 p bandwidth was found to be approximately 17eV. An observed dependence of the SXE spectra on the excitation energy is partly accounted for by a simple model that considers the presence of the two nonequivalent ET carbon sites. We also find evidence in the SXE spectra for a high degree of localization in the lowest unoccupied states.