Photon Factory Activity Report 2004 #22 Part B (2005)
Electronic Structure of Condensed Matter

28A

Fermi Surfaces and Kink in the Energy Dispersions of Sr2RuO4
Hideaki IWASAWA1, 2, Yoshihiro AIURA*2, Keijiro YAMAKAWA1, Tomohiko SAITOH1,Kanta ONO3, Masato KUBOTA3, Kenichi OZAWA4, Takafumi SATO5, Takashi TAKAHASHI5,6677Hiroshi KUMIGASHIRA , Masaharu OSHIMA , Teppei YOSHIDA , Atsushi FUJIMORI
1

Dept. of Applied Physics, Tokyo Univ. of Science, Shinjuku-ku, Tokyo 162-8601, JapanNational Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan
3
Institute of Materials Structure Science, Tsukuba, Ibaraki 305-0801, Japan
4
Dept. of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-0033, Japan
5
Dept. of Physics, Tohoku Univ., Sendai 980-8578, Japan
6
Dept. of Applied Chemistry, Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
7
Dept.of Physics and Dept. of Complexity Science and Engineering, Univ. of Tokyo, Tokyo, 113-0033, Japan
2Introduction
The sudden change of the group velocity, so-called the“kink”, of the dispersing peak in angle-resolved
photoemission spectroscopy (ARPES) spectra is widelyreported in the high-temperature superconducting
cuprates. Nevertheless, the interpretations of the kink forthe cuprates have been controversial. In previous works,electronic coupling to a bosonic mode such as phonons ormagnetic excitations has been discussed as the origin.
Recently, we have found a similar kink in the dispersionof the layered perovskite strontium ruthenates [1]. Thismeans that the kink is not peculiar to the cuprates. The
layered strontium ruthenates with perovskite-based
crystal structure are isostructural to the cuprates, whilethe electronic and magnetic properties are quite different.
The electronic structure close to the Fermi level (EF) of
the layered ruthenates is derived not only from the inplane Ru 4dxy−O 2p band but also from the out-of-planeRu 4dyz,zx−O 2p ones, while for the cuprates a single inplane Cu 3dx2-y2−O 2p band plays a crucial role. Therefore,
ARPES study on the layered ruthenates is expected toprovide insight into the origin of the kink in transition
metal oxides.
Experimental
The present measurements were carried out at a newhigh-resolution and high-flux undulator beamline (BL-28)
of the Photon Factory (KEK, Tsukuba). The sample
goniometer used here provides independent polar and tilt
rotations of the sample (R-Dec Co. Ltd., i GONIO LT)[2]. The beamline is equipped with a high-resolution,
hemispherical electron analyzer (Gammadata-Scienta,SES-2002). In order to obtain clean surfaces without thereplica of Fermi surface’s in the bulk due to the surface
rotation, we cleaved the single crystalline Sr2RuO4
samples in situ in ultrahigh vacuum at 160 K.

Fermi surfaces of Sr2RuO4. Since the Fermi surfaces are
qualitatively consistent with the LDA band prediction(white lines) and the previous ARPES measurement, we
judged that the sample quality is enough reliable toinvestigate the detailed band dispersions. Figures 1 (a)and (b) show the intensity plots along (0, 0)-(0, π) and (π,0)-(π, π), respectively. The measured momentum area
(black thick lines) is shown in Fig. 1 (c). A kink in thedispersion is clearly observed for the γ band, while not forthe α and β bands. The result will play a key role forunderstanding the origin of the kink.

FIG. 1 (a) and (b) Intensity plots along (0, 0)-(0, π) and(0, π)-(π, π), respectively. (c) EF intensity map. The
measured momentum area in (a) and (b) are shown by theblack thick lines. The white lines mean the Fermi surfaces
based on the LDA calculation. All spectra were taken at aphoton energy of 65 eV and at 30 K.
References[1] Y. Aiura et al., Phys. Rev. Lett. 93, 117005 (2004).
[2] Y. Aiura et al., Rev. Sci. Instrum. 74, 3177 (2003).
* y. aiura@aist.go.jp

Results and Discussion
In order to elucidate the origin of the kink, wemeasured ARPES spectra of Sr2RuO4 along the highsymmetry lines _M and MX. Figure.1 (c) shows the100Users' Report