Anomalous contribution to the nematic electronic states from the structural transition in FeSe revealed by time- and angle-resolved photoemission spectroscopy

TL;DR

This study uses advanced photoemission spectroscopy to reveal how structural transitions influence the electronic nematic states in FeSe, identifying two electronic phase transitions and their relation to structural changes above the superconducting temperature.

Contribution

It provides new insights into the impact of structural transitions on nematic electronic states in FeSe, highlighting the importance of the 120 K transition in electronic band development.

Findings

Two critical excitation fluences indicating electronic phase transitions.

Identification of two equilibrium electronic phase transitions at ~90 K and ~120 K.

An anomalous 10 meV contribution to nematic states from structural transition.

Abstract

High-resolution time- and angle-resolved photoemission measurements were made on FeSe superconductors. With ultrafast photoexcitation, two critical excitation fluences that correspond to two ultrafast electronic phase transitions were found only in the $d_{yz}$-orbit-derived band near the Brillouin-zone center within our time and energy resolution. Upon comparison to the detailed temperature dependent measurements, we conclude that there are two equilibrium electronic phase transitions (at approximately 90 and 120 K) above the superconducting transition temperature, and an anomalous contribution on the scale of 10 meV to the nematic states from the structural transition is experimentally determined. Our observations strongly suggest that the electronic phase transition at 120 K must be taken into account in the energy band development of FeSe, and, furthermore, the contribution of the structural transition plays an important role in the nematic phase of iron-based high-temperature superconductors.