PHOTOELECTRON SPECTROSCOPIC STUDY OF κ-(BEDT-TTF)2Cu(NCS)2 ORGANIC SUPERCONDUCTOR

Abstract

Experimental evidence for understanding the transport and electrical properties of the 10.4 K organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 (where BEDT-TTF represents bis(ethylenedithio)tetrathiafulvalene) has been achieved by X-ray and ultraviolet photoelectron spectroscopic (XPS and UPS) measurements. Chemical environment of the atoms in this organic superconductor is discussed based on the XPS core-level results. Binding energies of the inequivalent C and S sites in the cation BEDT-TTF and the anion Cu(NCS)2 are found to be different and an assignment is made. The valences of Cu and N were observed to be typically +1 and −3, respectively. The results indicate that bonding is somewhat covalent in the BEDT-TTF while it is ionic in the Cu(NCS)2, i.e., conduction in this compound occurs essentially on the two-dimensional network of the BEDT-TTF molecules. Measurements of the valence band region revealed a broad valence band structure with several peak features.