Photoemission studies on Fe(Se,Te) chalcogenides

The electronic structure of valence band and conduction band for FeSe1-xTex (x = 1, 0.5,0) have been probed using UV Photoemission and Inverse Photoemission respectively. The experimental results and the theoretical LDA+U band structure calculations show a doping dependent pseudogap with Se substitution both in the occupied and unoccupied electronic states. The temperature dependent spectral weight transfer near the Fermi level, which results in the pseudogap, in the valence band region has been correlated to the changes in Fe(Se,Te)4 tetrahedra which is sensitive to the change in chalcogen height i.e. the distance of chalcogen atom from the Fe plane. The calculations have shown that these structural changes lead to shifts in the electron occupancy from the xz/yz and x2-y2 orbitals to the 3z2-r2 orbitals indicating a temperature induced crossover from a metallic state to an Orbital Selective Mott (OSM) Phase. Our study presents an observation of a temperature induced crossover to a low temperature OSM phase in the family of Fe chalcogenides. Complementary changes were observed on the unoccupied side in our inverse photoemission study. The depletion in spectral weight from the near EF states at low temperature in IPES has been correlated with the enhancement of the 3z2-r2 orbitals in the PES. Changes in Fe-3d - chalcogen-p hybridisation originating from the changes in the chalcogen height due to doping and reduction in temperature controls the electronic structure of Fe superconductors. The coulomb correlation energy U, estimated from the combined PES and IPES spectra, signifies the enhancement in electron correlations in FeSe1-xTex, with doping. The formation of pseudogap in PES and IPES confirms the importance of correlations in the 11 family of Fe superconductors.

References:
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