Ultrafast nematic-orbital excitation in FeSe

TL;DR

This study uses femtosecond optical pulses and advanced spectroscopy to observe ultrafast, lattice-decoupled electronic nematic excitations in FeSe, revealing critical behavior and orbital imbalances.

Contribution

First real-time observation of ultrafast, lattice-decoupled electronic nematic excitations in FeSe using multi-dimensional photo-emission spectroscopy.

Findings

Nematicity disappears quickly after strong excitation.

Heavily damped oscillations of nematicity observed.

Critical behavior as a function of pump fluence.

Abstract

The electronic nematic phase is an unconventional state of matter that spontaneously breaks the rotational symmetry of electrons. In iron-pnictides/chalcogenides and cuprates, the nematic ordering and fluctuations have been suggested to have as-yet-unconfirmed roles in superconductivity. However, most studies have been conducted in thermal equilibrium, where the dynamical property and excitation can be masked by the coupling with the lattice. Here we use femtosecond optical pulse to perturb the electronic nematic order in FeSe. Through time-, energy-, momentum- and orbital-resolved photo-emission spectroscopy, we detect the ultrafast dynamics of electronic nematicity. In the strong-excitation regime, through the observation of Fermi surface anisotropy, we find a quick disappearance of the nematicity followed by a heavily-damped oscillation. This short-life nematicity oscillation is seemingly related to the imbalance of Fe 3dxz and dyz orbitals. These phenomena show critical behavior as a function of pump fluence. Our real-time observations reveal the nature of the electronic nematic excitation instantly decoupled from the underlying lattice.