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

2C/2005G101, 2005S2-002

In-situ photoemission study of Pr1−xCaxMnO3 epitaxial thin films
Hiroki WADATI*1, Atsushi MANIWA2, Isao OHKUBO2,Hiroshi KUMIGASHIRA2, 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
5
National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan
Introduction
Hole-doped perovskite manganese oxides R1-xAxMnO3,
where R is a rare-earth (R = La, Nd, Pr) and A is analkaline-earth atom (A = Sr, Ba, Ca), have attracted muchattention because of their remarkable physical properties
such as colossal magnetoresistance and the ordering ofspin, charge, and orbitals [1]. Half-doped manganites (x ~0.5) are particularly interesting because most of them
exhibit a CE-type charge-ordered (CO) state. The
compound Pr1-xCaxMnO3 (PCMO), where the bandwidth
W is smaller than the other manganites, has a particularly
stable CO state in the wide hole concentration range
between x ~ 0.3 and 0.75 [2]. In this study, in order toobserve how the electronic structure of PCMO changes
with hole doping, we have performed in-situ
photoemission spectroscopy and x-ray absorption
spectroscopy (XAS) measurements of epitaxial thin filmsof PCMO (x = 0.2 - 0.6) grown on LaAlO3 (001)substrates (which induces compressive strain) by laser
molecular beam epitaxy (laser MBE).
Experimental
The PCMO thin films were fabricated in a laser
MBEchamberconnectedtoasynchrotron
radiationphotoemission system at BL-2C of the Photon
Factory [3]. PCMO thin films were deposited on LaAlO3(001) substrates at 500 oC at an oxygen pressure of 1 × 104
Torr. The fabricated PCMO thin films were transferred-10
into the photoemission chamber under vacuum of 10Torr. The photoemission and XAS spectra were taken atroom temperature with the total energy resolution of
about 200 meV at the photon energy of 600 eV.
Results and Discussion
Figure 1 shows the doping dependence of the valenceband photoemission spectra. One can observe four main
structures, labeled as A, B, C, and D. From Mn 2p → 3d(643 eV) and Pr 3d → 4f (930 eV) resonant
photoemission spectra, structures A, B, C, and D are
assigned to Mn 3d eg, Mn 3d t2g plus Pr 4f, non-bonding O
2p, and Mn 3d - O 2p bonding states, respectively.
Satellite structures were not observed. With hole doping
structures A-D moved toward the Fermi level (EF) as in

the rigid-band picture, but there was no density of states
at EF for all values of x, suggesting a non-rigid-band
behaviour near EF with spectral weight transfer across EF.
From the binding-energy shifts of core levels, it was
found that the chemical potential was shiftedmonotonically without any sign of suppression. The
suppression of the chemical potential shift was observedin bulk samples of PCMO [4]. Since the electronic phaseseparation results in the pinning of the chemical potential,the monotonic chemical-potential shift of PCMO thinfilms suggests the absence of phase separation on a
microscopic scale as in the case of LSMO [5, 6]. Theabsence of chemical potential pinning is consistent withthe suppression of charge ordering under the compressive
strain from the LaAlO3 substrates.

Fig. 1: Valance-band photoemission spectra ofPr1-xCaxMnO3 epitaxial thin films.
References[1] Y. Tokura and N. Nagaosa, Science 288, 462 (2000).
[2] Y. Tomioka et al., Phys. Rev. B 53, 1689 (1996).
[3] K. Horiba et al., Rev. Sci. Instr. 74, 3406 (2003).
[4] K. Ebata et al., unpublished.
[5] J. Matsuno et al., Europhys.Lett. 59, 252 (2002).
[6] K. Horiba et al., Phys. Rev. B 71, 155420 (2005).
*wadati@wyvern.phys.s.u-tokyo.ac.jp

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