Strongly enhanced temperature dependence of the chemical potential in FeSe*

FeSe is a prime candidate to study the effects of high-temperature superconductivity and nematic ordering in the Fe-based superconductors, as it has a highly tunable superconducting onset and experiences a nematic phase transition without any accompanying antiferromagnetic phase. Given the theoretical interest in understanding these phenomena, an accurate model of the electronic structure is highly desirable.
To overcome the known limitations of ab-initio modelling in FeSe, we present a new set of hopping parameters for a 10-orbital tight binding model fitted directly to our latest angle-resolved photoemission spectroscopy (ARPES) data for the tetragonal phase of FeSe. This provides a quantitatively accurate description of the low-energy dispersions observed in FeSe.
Using this parameter set we predict a large rigid shift of the chemical potential as a function of temperature. We confirm this experimentally using high-resolution ARPES at the Diamond Light Source. This unexpectedly strong chemical potential shift has important implications for future theoretical models of superconductivity and of nematic ordering in FeSe.