P22S

Laser SARPES

Performance of laser-based SARPES
with micrometer spatial and vector spin resolution at HiSOR
A, B

Takuma Iwata, A T. Kousa, A Y. Nishioka, A K. Ohwada, C K. Sumida,D
E. Annese, A M. Kakoki, A, B K. Kuroda, E H. Iwasawa, C M. Arita, C S. Kumar,
A, B
A. Kimura, C K. Miyamoto and B, C T. Okuda
A

Grad. Sch. Adv. Sci. Eng., Hiroshima Univ. 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, JapanB
WPI-SKCM2., Hiroshima Univ., 2-313 Kagamiyama, Higashi-Hiroshima, Japan 739-0046
CHiSOR, Hiroshima Univ. 2-313 Kagamiyama, Higashi-Hiroshima 739-0046, JapanD
Brazilian Center for Research in Physics, Rua Dr. Xavier Sigaud 150,
Rio de Janeiro, RJ 22290-180, Brazil
E
Institute for Advanced Synchrotron Light Source, National Institutes for Quantum Science andTechnology, Sendai 980-8579, Japan

Keywords: Spin-and angle-resolved photoemission spectroscopy, electronic structure, spin polarization, momentum space

Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to directory observe the electronicstructure of solids. In recent years, micro-ARPES [1] which is combined with a micro-focused light source
has attracted much attention, since it is found to very useful to explore the electronic states in newly
topological materials [2], phase-separated correlated systems [3] and transcription samples [4].
Spin-resolved ARPES (SARPES) [5] enables us to detect not only the energy and momentum but also thespin of photoelectrons owing to recent development of the spin detectors. However, micro-SARPES
measurement has never been reported so far, because of the difficulties of the spin detection and its
combination technique. Synchrotron Radiation is a conventional light source used for SARPES. Although
there are some synchrotron radiation based micro- (or nano-)ARPES systems, the use of special opticalelements (such as Fresnel zone plate) attenuate intensity of light and the need for a mechanism to control theoptical system under ultrahigh vacuum condition make micro-SARPES a difficult and still developing
technology.
In this context, we employed a high-photon flux ultraviolet laser with 6-eV of photon energy instead ofsynchrotron radiation to realize micro-SARPES. In addition to high photon flux, the advantage of the 6-eVlaser is the flexibility of its optical system due to high atmospheric transmission. Since SARPES requires anintense light source to perform high resolution measurements, we considered a laser to be the best lightsource for micro-SARPES. Therefore, we combined a high-intensity 6-eV laser with a high-efficiency spin
detector at HiSOR to develop micro-SARPES machine that can perform high-efficiency spin-resolved
experiments while maintaining micro-focusing.
In this presentation, we will describe the performance of the-state-of-the-art micro-SARPES machine
combining 6-eV laser source and the photoelectron analyzer equipped with the electron deflector function
and two VLEED type spin detectors [6]. We evaluated spatial resolution and long-time stability using an Au
polycrystalline letter pattern (“µ-SARPES”) sample, which is fabricated on a Si substrate using photolithography (Fig. 1). We performed not only 3D spin-resolved experiment to Bi2Te3, which is a typical
topological insulator as a test sample, but also spin- and spatial-resolved experiment to PbBi4Te4S3 [7], which
has two Dirac-cone-like dispersions derived from two distinct terminations (Fig. 2).

FIGURE 1. Characterization of the spatial resolution. (a) The optical microscope image of the Au pattern on the Si (001)substrate. (b) The image of the scanning photoelectron intensity map (SPEM) taken in the Au pattern. (c) and (d) Photoelectron
intensity profiles at the edges of the Au pattern along the x (horizontal) and y (vertical) axes, respectively (green and blue lines
in the insets). (e) Plots of the intensity deviation ΔI(x) and ΔI(y) as a function of time to evaluate possible long-term drifts ofthe laser and the sample stage. The data was recorded at the intensity edge at xc and yc denoted by arrows in (c) and (d). The
1~µm of the drift along x (y) axis can correspond to 19% (10%) of ΔI(x); [ΔI(y)] guided by dashed lines.

FIGURE 1. Demonstration of spatially-resolved SARPES measurements on PbBi4Te4S3 (a) Optical microscope image of acleaved surface of PbBi4Te4S3. (b) SPEM image taken with a 50 µm step. (c) Spatially-resolved ARPES images acquired atdifferent surface terminations [7]. (d) Scanning ARPES intensity map measured at the 100×100 µm marked by the red squarein (b). The map is taken by scanning 2 µm and 10 µm steps along x and y axes, respectively.

REFERENCES[1] H. Iwasawa et. al., Ultramicroscopy, 182, 85 (2017).
[2] R. Noguchi et al., Nature, 566, 518 (2019).
[3] K. Kuroda et al., Nature Communications, 11, 2888 (2020).
[4] I. Cucchi et al., Nano Letters, 19, 554 (2019).
[5] T. Okuda et. al,. J. Phys.: Condens. Matter, 29, 483001 (2017).
[6] T. Iwata et. al., Scientific Reports, 14, 127 (2024)[7] K. Sumida et. al., Physical Review materials, 2, 104201 (2018)