Photoinduced possible superconducting state with long-lived disproportionate band filling in FeSe

Shigeru Kasahara,Masami Fujisawa,Shik Shin,Kozo Okazaki,Nobuhisa Ishii,Mari Watanabe,Takeshi Suzuki,Takahiro Hashimoto,Teruto Kanai,Takashi Someya,Shoya Michimae,Yuji Matsuda,Jiro Itatani,Takasada Shibauchi

doi:10.1038/s42005-019-0219-4

Shigeru Kasahara, Masami Fujisawa + Show 12 more

Open Access

https://doi.org/10.1038/s42005-019-0219-4

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Journal: Communications Physics	Publication Date: Sep 25, 2019
Citations: 29	License type: open-access

Affiliation: Kyoto University, The University of Tokyo

Abstract

Photoexcitation is a very powerful way to instantaneously drive a material into a novel quantum state without any fabrication, and variable ultrafast techniques have been developed to observe how electron, lattice, and spin degrees of freedom change. One of the most spectacular phenomena is photoinduced superconductivity, and it has been suggested in cuprates that the transition temperature Tc can be enhanced from the original Tc with significant lattice modulations. Here, we show a possibility for another photoinduced high-Tc superconducting state in the iron-based superconductor FeSe. The transient electronic state over the entire Brillouin zone is directly observed by time- and angle-resolved photoemission spectroscopy using extreme ultraviolet pulses obtained from high harmonic generation. Our results of dynamical behaviors from 50 fs to 800 ps consistently support the favourable superconducting state after photoexcitation well above Tc. This finding demonstrates that multiband iron-based superconductors emerge as an alternative candidate for photoinduced superconductors.

Highlights

Photoexcitation is a very powerful way to instantaneously drive a material into a novel quantum state without any fabrication, and variable ultrafast techniques have been developed to observe how electron, lattice, and spin degrees of freedom change
For the excitation employed in most studies, a mid-infrared pulse is used to resonantly excite the lattice degree of freedom
The eventual lattice modulation playing a decisive role in photoinduced superconductivity was found to be the Raman-active Ag phonon, which is nonlinearly coupled to the photoexcited infrared-active phonon mode[11]

Summary

Introduction

Photoexcitation is a very powerful way to instantaneously drive a material into a novel quantum state without any fabrication, and variable ultrafast techniques have been developed to observe how electron, lattice, and spin degrees of freedom change. We show a possibility for another photoinduced high-Tc superconducting state in the iron-based superconductor FeSe. The transient electronic state over the entire Brillouin zone is directly observed by time- and angle-resolved photoemission spectroscopy using extreme ultraviolet pulses obtained from high harmonic generation. The dramatic increase in Tc for single-layer FeSe is accompanied by the disappearance of the hole Fermi surface (FS) and the increase in the electron FS7 In this context, photoexcitation has substantial advantages over other methods because it can instantaneously manipulate a material of interest in situ without any fabrication[8,9,10]. One of the striking phenomena is the photoinduced superconductivity reported in high-Tc cuprate superconductors, where the key mechanism is the lattice modulation[11]. This is overcome by using high harmonic generation (HHG) to obtain higher photon energy and capture a larger region of the Brillouin zone[21]

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Results

Conclusion