Nematic electronic state of the superconducting FeSe

A nematic state is a form of electronic order which breaks the rotational symmetries without changing the translational symmetry of the lattice, and this state may play an important role in understanding high temperature superconductivity. We have revealed the existence of a novel electronic state in an highly unconventional multiband superconductor, FeSe, from the evolution of its electronic structure from the high-temperature tetragonal phase into the electronic nematic phase using angle resolved photoemission spectroscopy (ARPES). By combining the findings of the low temperature electronic structure from ARPES and quantum oscillations we have established for the fisrt time that FeSe contains at least three different bands: two electron-like and one hole band. The ARPES experiments were performed at the Diamond Light Source and they were complemented with low temperature quantum oscillations studies suing European High Magnetic Field Laboratory at HMFL in Nijmegen and elastoresistance studies in Oxford. The single crystals were grown in the Clarendon Laboratory and the results of our finding were published as an Editor's Suggestion in Phys. Rev. B 91, 155106 (2015).