Isoelectronic substitution is an ideal tuning parameter to alter electronic states and correlations in iron-based superconductors. As this substitution takes place outside the conducting Fe planes, the electronic behaviour is less affected by the impurity scattering and relevant key electronic parameters can be accessed. In talk I present the experimental progress made in understanding the electronic behaviour of the nematic electronic superconductors, FeSe1−x Sx and FeSe1−xTex using angle-resolved photoemission spectroscopy. A direct signature of the nematic electronic state is the in-plane anisotropic distortion of the Fermi surface triggered by orbital ordering effects and electronic interactions that result in multi-band shifts of the different electronic bands. The changes in the electronic structure and their correlations with the superconducting phase diagrams will be discussed.

Keywords: Iron-based superconductors, ARPES