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

1C/2002S2-002

In-situ angle-resolved photoemission study of La1-xSrxFeO3 epitaxial thin films
Hiroki WADATI*1, Akira CHIKAMATSU2, Masaru TAKIZAWA1, Ryuji HASHIMOTO2,Hiroshi KUMIGASHIRA2, Takashi MIZOKAWA1, Atsushi FUJIMORI1, Masaharu OSHIMA2,Mikk LIPPMAA3, Masashi KAWASAKI4, Hideomi KOINUMA5
1
Department of Physics and Department of Complexity Science and Engineering,
University of Tokyo, Kashiwa 277-8561, Japan2
Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
3
Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan
4
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
5Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
Introduction
Angle-resolved photoemission spectroscopy (ARPES)
has long played a central role in studying the electronic
properties of strongly correlated electron materials with alayered perovskite structure. In contrast, there have beenfew studies on transition metal oxides with the threedimensional perovskite structure because they do nothave any cleavage plane. In this work, we have performed
in-situ ARPES measurements of single-crystal thin filmsof La1-xSrxFeO3 (LSFO). By performing in-situ studies, nocleaning procedures were necessary and we succeeded inobserving energy band dispersions in LSFO (x = 0.4).
Experimental
The LSFO thin films were fabricated in a laser MBE
chamber connected to a synchrotron radiation photoemission system [1]. The experiment was done at BL-1Cof Photon Factory. LSFO thin films were deposited on
Nb-doped TiO2-terminated SrTiO3 (001) substrates [2] ato-4950 C at an oxygen pressure of 1×10 Torr. Thefabricated LSFO thin films were transferred into thephotoemission chamber under an ultrahigh vacuum of 1010Torr. The PES spectra were taken at room temperature
with the total energy resolution of about 150 meV. Before
taking the ARPES spectra, we checked the surface
cleanliness of the samples by measuring LEED patterns.
1×1 spots were clearly observed, indicating that thesurface of the fabricated LSFO thin film was cleanenough.
Results and DiscussionFigure 1 shows the experimental band structure ofLSFO (x=0.4) thin films obtained by ARPES
measurements taken at hν = 74 eV. Here, the second
derivatives of the energy distribution curves (EDC’s) areplotted on the grey scale, and dark parts correspond toenergy bands. The dispersions of the Fe 3d eg, Fe 3d t2g,and O 2p bands could be observed. The observed eg band
did not cross the Fermi level (EF), consistent with thepersistence of the gap as observed in angle-integrated
photoemission spectra [3]. The band dispersions arecharacteristics of the G-type antiferromagnetic (AF) staterealized in this system. In order to interpret the band

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Users' Reportstructure quantitatively, we have performed a tightbinding model calculation. Here, the effect of G-type AF
is taken phenomenologically by making the energy
difference ∆E between the spin-up and spin-down sites.
The red dots in Fig. 1 show the result of this calculation,
which reproduces the experimental band structure fairly
well. However, the EF position determined from thefilling of electrons was not in agreement with theexperimental EF because of the insulating behaviour of
this material. We consider that the insulating behaviour of
this material is caused by localized holes observed by O
1s XAS [3], a polaronic effect, which is also observed inother transition-metal oxides like Fe3O4 [4], and/or local
charge disproportionation [5].

Fig. 1:
Experimental band structure of LSFO (x = 0.4) obtainedby ARPES measurements taken at hν = 74 eV. Dark parts
correspond to energy bands. Red dots show the band
dispersion obtained by tight-binding calculation.
References[1] K. Horiba et al., Rev. Sci. Instr. 74, 3406 (2003).
[2] M. Kawasaki et al., Science 266, 1540 (1994).
[3] H. Wadati et al., Phys. Rev. B 71, 035108 (2005).
[4] D. Schrupp et al., cond-mat/0405623.
[5] M. Takano et al., J. Solid State Chem. 39, 75 (1981).
* wadati@wyvern.phys.s.u-tokyo.ac.jp