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Abstract. Our valence band photoelectron spectroscopic studies show a temperature dependent spectral weight transfer near the Fermi level in the Fe-based superconductor FeSe 1−x Te x . Using theoretical band structure calculations we have shown that the weight transfer is due to the temperature induced changes in the Fe(Se,Te) 4 tetrahedra. These structural changes lead to shifts in the electron occupancy from the xz/yz and x 2 -y 2 orbitals to the 3z 2 -r 2 orbitals indicating a temperature induced crossover from a metallic state to an Orbital Selective Mott (OSM) Phase. Our study presents the observation of a temperature induced crossover to a low temperature OSM phase in the family of Fe chalcogenides.

Temperature (12K ≤ T ≤ 300K) dependent extended X-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe 1−x Te x (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for increase in T C upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe 0.5 Te 0.5 , they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe 0.5 Te 0.5 , near superconducting onset, the two heights, h F e−Se and h F e−T e show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides. PACS numbers:

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