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.
Highlights
The electronic nematic phase is an unconventional state of matter that spontaneously breaks the rotational symmetry of electrons
We discuss the nematic-orbital excitation obtained in the present Time-resolved ARPES (TARPES) results by comparing with the nematic dynamics in thermal equilibrium as probed by recent Raman scattering measurements[15,30]
The quasi-elastic peak (QEP) rapidly diminishes at T < Ts, on the other hand, and a gap opens in the XY Raman spectra, indicating the suppression of low-energy nematic excitations[30]
Summary
The electronic nematic phase is an unconventional state of matter that spontaneously breaks the rotational symmetry of electrons. 1234567890():,; Iron-based superconductors exhibit attractive properties such as high-transition-temperature (Tc) superconductivity and complex competing phases[1] Their electronic structures consist of multiple iron 3d orbitals, giving rise to a variety of antiferroic and ferroic ordering phenomena involving spin and orbital profiles[2,3,4]. A wide range of materials have been investigated for clarifying their electronic dynamics, such as the recombination of the superconducting quasiparticles[21,22], fluctuating charge density waves[23], collapse of long-range order[24,25], and coupling with optical phonons[25,26,27] These results, which are inaccessible from equilibrium state, contributed to the deeper understanding of exotic quantum states, especially those with short lifetimes. With this TARPES setup[28] (Fig. 1e), the ultrafast dynamics of the nematic Fermi surface and the orbital-dependent carrier dynamics can be visualized
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