HiSORセミナー
Putting more information on spin-ARPES: from meV energy-resolution to fs time-resolution
日時 2021年7月26日 （月） 13：00-14：10頃
場所 オンライン(Zoom形式)
講師 Kenta Kuroda
(The Institute for Solid State Physics, The University of Tokyo)
Spin- and angle-resolved photoemission spectroscopy (spin-ARPES) is a powerful technique to reveal various information about the occupied electronic states in solids [1]. In addition to this capability, a combination of spin-ARPES with pump-probe laser techniques makes it possible to image the optically excited electron population into the unoccupied bands in k-space and follow the ultrafast charge and spin dynamics in the time domain, which can be useful for studying novel optical responses of quantum materials. However, this combination technique is rather challenging. The main reasons are two. The one is that the efficiency of the spin detection is very low [2] and thus one needs more photons. The second is that high-energy photons are necessary to cover a wide k range, which can be produced by higher harmonic generations. However, photon flux sufficient to overcome the low spin-detection efficiency leads to a large space charge effect in photoemission experiments, and thus one should reduce the photon flux [3]. These two are in a serious dilemma.
In this seminar, I will talk about a state-of-the-art pump-probe spin-ARPES apparatus constructed at ISSP, The University of Tokyo [4]. This apparatus is based on our spin-ARPES system [5] equipped with the highly efficient very-low-energy-electron-diffraction (VLEED) spin detectors as well as high-resolution 7-eV laser . To combine it for pump-probe spin-ARPES, we choose 10.7-eV laser pulses at the high repetition rate (1-MHz), which is based on a Yb: fiber chirped-pulse amplifier laser [6]. This combination overcomes the above dilemma and enables us to obtain the large signals enough to observe the unoccupied spin-polarized bands in various materials and their ultrafast dynamics. Finally, I will compare kHz-class and MHz-class laser set-up for future pump-probe experiments.
[1] T. Okuda and A. Kimura, J. Phys. Soc. Jpn. 82, 021002 (2013).
[2] T. Okuda, J. Phys. Condens. Matter 29, 483001 (2017).
[3] L.-P. Oloff et al., J. Appl. Phys. 119, 225106 (2016).
[4] K. Kawaguchi, K. Kuroda et al., in preparation
[5] K. Yaji et al., Rev. Sci. Instrum. 87, 053111 (2016).
[6] Z. Zhao et al., Opt. Exp. 25, 13517 (2017).
問合せ先 出田真一郎（放射光科学研究センター）
