Ultrafast nematic-orbital excitation in FeSe

ROM 2019-05
Author: Takahiro Shimojima (email takahiro.shimojima@riken.jp)
Institute: http://www.riken.jp/en/research/labs/cems/electron_states_spectro/
Publication: Nature Comm 10, 1946 (2019), DOI: 10.1038/s41467-019-09869-5
Instrument: ARPES-Lab

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.

T. Shimojima1,2, Y. Suzuki2, A. Nakamura1,2, N. Mitsuishi2, S. Kasahara 3, T. Shibauchi 4, Y. Matsuda 3, Y. Ishida5, S. Shin 5 & K. Ishizaka1,2

1) RIKEN Center for Emergent Matter Science (CEMS), Wako 351-0198, Japan.
2) Quantum-Phase Electronics Center (QPEC) and Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan.
3) Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
4) Department of Advanced Materials Science, The University of Tokyo, Kashiwa 277-8561, Japan.
5) Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa 277-8581, Japan.