ARPES probe of the electronic structure in the detwinned FeSe

The nature of the nematic order remains to be an important issue for a comprehensive understanding of phase competition in iron-based superconductors and has strong implications on the mechanism of high temperature superconductivity. However, the strong coupling between the nematic order and spin density wave order makes it very challenging to disentangle the contribution from the orbital and magnetic degree of freedom in iron pnictides. FeSe, due to the lack of long range magnetic order, is an ideal system for isolating the contribution of nematicity to the fundamental physics of the iron-based superconductors. Angle-resolved photoemission spectroscopy (ARPES) has played a critical role in unveiling the strong in-plane orbital anisotropy associated with the nematic order in iron pnictide compounds. On the other hand, conflicting results on the magnitude of nematic splitting in FeSe have been reported.

I will present our latest ARPES data taken on fully detwinned FeSe single crystals. The high quality single-domain data allow us to unambiguously identify the orbital character of the observed bands and confirm a momentum dependent nematic splitting between dxz and dyz bands that is consistent with the previous understanding of an electronically-driven nematic order in iron pnictide superconductors. Furthermore, our data reveals the 2nd electron pocket with missing dxz spectral weight, providing a natural explanation for the orbital selective quasiparticle interference in FeSe.