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

2C/2003G149

In-situ photoemission study of Nd1-xSrxMnO3 epitaxial thin films
Hiroki WADATI*1, Riichiro TAKAISHI2, Akira CHIKAMATSU2, Masaru TAKIZAWA1,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
Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
Introduction
Hole-doped perovskite manganese oxides R1-xSrxMnO3(R = rare earth) have attracted much attention because of
their interesting magnetic and transport properties such as
colossal magnetoresistance and metal-insulator transition[1]. Among them, Nd1-xSrxMnO3 (NSMO) is especiallyinteresting because for x = 0.5 it undergoes a transition
from the ferromagnetic metal (FM) to a charge-orderedinsulator (COI) upon cooling [2]. In this study, we have
performed in-situ photoemission spectroscopy (PES) andx-ray absorption spectroscopy (XAS) measurements ofepitaxial thin films of NSMO (x = 0, 0.2, 0.4, 0.55) grown
on SrTiO3 (001) substrates. We have succeeded inobtaining bulk-sensitive high-quality spectra by using soft
x-rays and atomically flat surfaces of the thin films.

A becomes weaker with increasing x, indicating that holes
are doped into the eg band.
From the binding-energy shifts of core levels, it was
found that the chemical potential is shifted monotonicallywithout any sign of suppression. The values of the shifts
are almost the same as those of La1-xSrxMnO3 [5, 6]. Since
the electronic phase separation results in the pinning of
the chemical potential, the monotonic chemical-potential
shift of NSMO suggests the absence of phase separation
on a microscopic scale as in the case of LSMO. This
result is considered to reflect the narrower composition
range of charge-ordered states than that of, for example,
Pr1-xCaxMnO3, which shows charge ordering over a wide
composition range around x = 0.5.

Experimental
The NSMO thin films were fabricated in a laser MBEchamber connected to a synchrotron radiation photoemission system at BL-2C of Photon Factory [3]. NSMO
thin films were deposited on Nb-doped TiO2-terminatedoSrTiO3 (001) substrates [4] at 1050 C at an oxygen-4
pressure of 1×10 Torr. The fabricated NSMO thin films
were transferred into the photoemission chamber under an-10
ultrahigh vacuum of 10 Torr. The PES spectra weretaken at room temperature with the total energy resolutionof about 200 meV at the photon energy of 600 eV.
Results and Discussion
Figure 1 shows the doping dependence of the valenceband PES spectra. One can observe four main structures,
labeled as A, B, C, and D. From Mn 2p → 3d (643 eV)
and Nd 3d → 4f (979 eV) resonant photoemission spectra,structures A and B are ascribed to the Mn eg and t2g states,
respectively, and structures C and D are ascribed to theMn 3d - Nd 4f - O 2p mixed states. A gap (absence offinite density of states at EF) is seen for all values of x,
which is considered to be a natural consequence of theinsulating behavior of this system at room temperature.
The satellite structures are not observed. Structures A-D
move toward EF upon hole-doping. In addition, structure

Fig. 1: PES spectra of NSMO epitaxial thin films.
References[1] M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod. Phys.
70, 1039 (1998), and references therein.
[2] H. Kuwahara et al., Science 270, 961 (1995).
[3] K. Horiba et al., Rev. Sci. Instr. 74, 3406 (2003).
[4] M. Kawasaki et al., Science 266, 1540 (1994).
[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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