Orbital Degeneracy, Jahn–Teller Effect, and Superconductivity in Transition-Metal Chalcogenides

Abstract

We have studied the electronic structure of FeSe1−xTex and Ir1−xPtxTe2 using photoemission spectroscopy. For FeSe1−xTex, angle-resolved photoemission results indicate that the Fe 3d yz/zx orbital degeneracy at Γ point and orbitally induced Peierls effect in the tetragonal lattice play important roles for the superconductivity. It is suggested that the Jahn-Teller instability of the yz/zx states couples with local lattice distortion derived from the Te substitution for Se and provides an inhomogeneous electronic state. Photoemission results of IrTe2 with triangular lattice are also consistent with the orbitally induced Peierls scenario. The Pt substitution for Ir suppresses the static band Jahn–Teller effect and induces an inhomogeneous electronic state in which orbital (or bond or nematic) fluctuations may help superconductivity through the Peierls effect.