Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

2C/2005S2-002

In situ synchrotron-radiation photoemission spectroscopic studyof strain-controlled La0.6Sr0.4MnO3 thin films
121*
Atsushi MANIWA1, Akira CHIKAMATSU, Hiroki WADATI, Hiroshi KUMIGASHIRA,
1
2
3
Masaharu OSHIMA , Atsushi
FUJIMORI,Mikk
LIPPMAA,
Masashi KAWASAKI4, and Hideomi KOINUMA5
1
Department
of Applied Chemistry, The University of Tokyo, Tokyo 113-8656, Japan2
Department of Complexity Science and Engineering, The University of Tokyo,
Kashiwa 277-8561,Japan3
InstituteforSolidStatePhysics,
The University of Tokyo, Kashiwa 277-8581, Japan
4InstituteforMaterials
Research,Tohoku University, Sendai 980-8577, Japan
5National Institute for Material Science, Tsukuba 305-0047, Japanof the eg state shifts to the higher binding energy side by
100 meV from LSMO/LSAT (strain free) to LSMO/LAO(compressive strain). The shift of eg state is more clearlyseen in the expansion near EF (inset). The energy shift ofeg state in LSMO/LAO is explained by the energy
222 2
splitting of degenerated eg state to d(x -y ) and d(3z -r )states due to the Jahn-Teller distortion induced by the3compressive epitaxial strain. The results suggest that theresultant formation of energy gap at EF is responsible forthe strain-induced metal-insulator transition in the straincontrolled LSMO.

LSMO thin films
Ahν = 600 eV

T = 300 K

LSMO/LAO
LSMO/LSAT
LSMO/STO

B

Intensity (arb. units)

Introduction
Hole-doped perovskite manganese oxides La1-xSrxMnO3(LSMO) have attracted much attention because of theirinteresting magnetic and electronic properties such as
colossal magnetoresistance, half-metallicity, and metalinsulator transition. The extensive studies havedemonstrated that the physical properties of these1
manganese oxides can be controlled by epitaxial strain.
However, little is known on the effects of epitaxial strain
on the electronic structure of these films. In this study,
we report in situ photoemission (PES) study of LSMO (x= 0.4) thin films deposited on LaAlO3 (LAO) with latticemismatch of – 2 %, (LaAlO3)0.3-(SrAl0.5Ta0.5O3)0.7 (LSAT)with that of + 0 %, and SrTiO3 (STO) with that of + 1 %substrates to investigate the changes in the electronic
structure of LSMO thin films.
Experimental
The strain-controlled LSMO (x = 0.4) has been
epitaxially grown on LAO, LSAT, and STO substrates ina laser MBE chamber connected to a synchrotron
2radiation PES system at BL2C of the Photon Factory.
The film thickness was estimated to be 40 nm bymonitoring the intensity of the specular spot in reflection
high-energy electron diffraction (RHEED) patterns. The
coherent growth of these films was confirmed by thefour-circle X-ray diffraction measurements. The PES
spectra were taken in situ with a total energy resolution of150 meV in the photon energy range of 600-700 eV.
Results and Discussion
Figure 1 shows the valence band photoemission spectraof LSMO thin films under different epitaxial strain fromdifferent substrates, where LSMO/STO and LSMO/LSAT
are ferromagnetic metal, while LSMO/LAO is
antiferromagnetic insulator. The valence band spectra
consist of four main structures labelled as A, B, C, and D.
3From the band structure calculation , the two prominent
structures A and B are assigned to O 2p states, while ashoulder structure C and a broad hump structure D closest
to the Fermi level (EF) are assigned to Mn 3d t2g and egstates, respectively. At the first glance, the overall valenceband structure does not seem to change with epitaxial
strain. However, closer look reveals that the peak position

CD

1.0
1.0

0.5
0.5
B. E (eV)B. E. (eV)

10866

40.0

EF

20EF

Binding Energy (eV)Fig. 1: The valence band spectra of LSMO thin films onvarious substrates. Inset shows the spectra near EF.
References[1] Y. Konishi et al., J. Phys. Soc. Jpn 68, 3790 (1999).
[2] H. Kumigashira et al., Appl. Phys. Lett. 82, 3430
(2003).
[3] Z. Fang et al., Phys. Rev. Lett. 84, 3169 (2000).
* kumigashira@sr.t.u-tokyo.ac.jp

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