Distinctive momentum dependence of the band reconstruction in the nematic state of FeSe thin film

TL;DR

This study reveals that in FeSe thin films, the nematic state involves a momentum-dependent band splitting linked to anisotropic nearest-neighbor hopping, providing insights into the non-magnetic origin of nematicity in iron-based superconductors.

Contribution

The paper demonstrates that the band reconstruction in FeSe's nematic state is strongly momentum dependent and cannot be explained by simple ferro-orbital ordering, highlighting the role of anisotropic hopping.

Findings

Nematic transition occurs at ~125 K without magnetic order.

Largest band splitting (~80 meV) at the zone corner.

Anisotropic nearest-neighbor hopping explains the momentum dependence.

Abstract

Nematic state, where the system is translationally invariant but breaks the rotational symmetry, has drawn great attentions recently due to experimental observations of such a state in both cuprates and iron-based superconductors. The mechanism of nematicity that is likely tied to the pairing mechanism of high-Tc, however, still remains controversial. Here, we studied the electronic structure of multilayer FeSe film by angle-resolved photoemission spectroscopy (ARPES). We found that the FeSe film enters the nematic state around 125 K, while the electronic signature of long range magnetic order has not been observed down to 20K indicating the non-magnetic origin of the nematicity. The band reconstruction in the nematic state is characterized by the splitting of the dxz and dyz bands. More intriguingly, such energy splitting is strong momentum dependent with the largest band splitting of ~80meV at the zone corner. The simple on-site ferro-orbital ordering is insufficient to reproduce the nontrivial momentum dependence of the band reconstruction. Instead, our results suggest that the nearest-neighbor hopping of dxz and dyz is highly anisotropic in the nematic state, the origin of which holds the key in understanding the nematicity in iron-based superconductors.