Surface electronic structure of the organic superconductor κ-(ET)2Cu(NCS)2 studied via photoemission microscopy

The surface electronic structure of cleaved single crystals of the organic superconductor κ-(ET)2Cu(NCS)2 has been studied using photoemission microscopy. Two types of cleaved surfaces were observed, displaying different valence band photoemission spectra and different spectral behavior near the Fermi level, EF. In particular, spectra from one surface type display relatively broad spectral features in the valence band and finite spectral intensity at EF, while spectra from the other surface type show well-defined valence band emission features and zero photoemission intensity at EF. We propose that the spectral differences are due to a very short electron mean free path in this material, and our results are used to explain the differences between previously published photoemission spectra from this superconductor. We also report the results of an investigation of the electronic structure of defects in this material.