Importance of ligands in the electronic properties of FeTe0.6Se0.4

We investigate the electronic structure of FeTe0.6Se0.4 employing high resolution photoemission spectroscopy and ab initio band structure calculations. Fe 2p core level and the valence band spectra exhibit signature of strong electron correlation in the electronic structure. The electronic states near the Fermi level reduces in intensity with the decrease in temperature in conformity with the insulating transport observed near 300 K. An insulator to metal transition around 150 K could be related to the spectral lineshape change in the vicinity of the Fermi level. The spectral features near Fermi level exhibit significant p orbital character due to the correlation induced Fe d spectral weight transfer. The experimental spectra reveal dominant temperature dependence of the spectral functions possessing large p-character. While the origin of the anomalous electronic properties in the normal phase could be revealed in the electronic structure of this material, these results emphasizes the importance of ligand states in the high temperature superconductors that is important to explore such materials for various applications. (C) 2013 AIP Publishing LLC.