Effects of strain on the electronic structure, superconductivity, and nematicity in FeSe studied by angle-resolved photoemission spectroscopy

Abstract

One of central issues in iron-based superconductors is the role of structural change to the superconducting transition temperature (${T}_{c}$). It was found in FeSe that the lattice strain leads to a drastic increase in ${T}_{c}$, accompanied by suppression of nematic order. By angle-resolved photoemission spectroscopy on tensile- or compressive-strained and strain-free FeSe, we experimentally show that the in-plane strain causes a marked change in the energy overlap ($\mathrm{\ensuremath{\Delta}}{E}_{h\ensuremath{-}e}$) between the hole and electron pockets in the normal state. The change in $\mathrm{\ensuremath{\Delta}}{E}_{h\ensuremath{-}e}$ modifies the Fermi-surface volume, leading to a change in ${T}_{c}$. Furthermore, the strength of nematicity is also found to be characterized by $\mathrm{\ensuremath{\Delta}}{E}_{h\ensuremath{-}e}$. These results suggest that the key to understanding the phase diagram is the fermiology and interactions linked to the semimetallic band overlap.