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

2C/2005G101

Spectral weight transfer in Pr1-xCaxMnO3 studied by photoemission spectroscopy

11Kazuaki EBATA*1, Hiroki2WADATI1, Masaru TAKIZAWA, Atsushi FUJIMORI
2
2
Akira CHIKAMATSU , Hiroshi KUMIGASHIRA, Masaharu
OSHIMA ,33, 4, 5,
Yoshinori
TOKURA,Yasuhide
TOMIOKA1
Department of Complexity Science and Engineering and Department of Physics,
University of Tokyo, Kashiwa, Chiba, 277-8561, Japan2
Department of Applied3 Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
Correlated Electron Research Center (CERC),
National
InstituteofAdvanced
Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan
4
DepartmentofAppliedPhysics,
University of Tokyo Bunkyo-ku, Tokyo 113-8656, Japan
5
Spin Superstructure Project, Exploratory Research for Advanced Technology (ERATO),
Japan Science and Technology Corporation (JST), Tsukuba 305-8562, Japan

98

Users' Reportrespectively, consistent with the cluster-model calculation
for La1-xSrxMnO3 (LSMO) [2].
Figure 1(b), 1(c) shows the valence-band spectra near
Fermi level (EF) for various hole concentrations taken athν = 21.2 eV and 600 eV, respectively. The spectra havebeen normalized to the integrated intensity in the energy
range from 1.5 eV to ~EF. Two features labeled D’ and D”
were observed in these spectra. Spectral weight wastransferred from D’ to D” with increasing holeconcentration, that is, the valence-band spectra near EF
exhibited highly non-rigid-band-like behavior, similar tothat in the LSMO [2].
C"(a)Pr1-xCaxMnO 3
Pr 3 d - 4 f resonanceIntensity (arb. units)

Introduction
In recent decades, manganites have been extensively
studied because of their remarkable physical properties
such as colossal magnetoresistance (CMR) and spin,
charge and orbital ordering. The compound Pr1-xCaxMnO3(PCMO), in which the band-width W is small incomparison with other manganites, has a particularly
stable charge ordered (CO) state [1]. Furthermore, CMR
in the CO state of PCMO has been remarkable,amounting to several orders magnitude [1]. In this paper,
we report on the composition dependence of the valenceband spectra in single crystals of PCMO.
Experimental
Single crystals of PCMO with the carrier
concentrations of x = 0.2, 0.25, 0.3, 0.45, 0.5 and 0.65
were grown by the floating-zone method. The
photoemission spectroscopy (PES) measurements wereperformed at BL-2C of Photon Factory, High Energy
Accelerators Research Organization (KEK) using photon
energy of hν = 600 eV, 643.6 eV (Mn2p-3d resonance),
930 eV (Pr 3d-4f resonance). Ultraviolet photoemission
spectroscopy (UPS) was also performed using the photon
energy hν = 21.2 eV. All the measurements wereperformed under the base pressure of ~10-10 Torr at room
temperature. Clean surfaces were obtained by repeated insitu scraping with a diamond file.
Results and Discussion
Valence-band spectra of PCMO taken at different
photon energies are shown in Fig. 1(a). The spectra
mainly consisted of structures as labeled A, A’, B, C, C’,C”, and D. The spectra taken at hν = 930 eV and 643.6
eV correspond to Pr 3d-4f and Mn 2p-3d on-resonant PES
spectra, respectively. From the Mn 2p-3d resonancespectra, Mn 3d-derived features appeared as structures A’,C’, and D. Structures A’ and C’ are shifted slightly towardhigher binding energies than A and C, respectively, due tothe different matrix elements between normal PES andresonant PES. Also, the intensity of structure C” wasstrongly enhanced in the Pr 3d-4f resonance spectra. TheUPS (hν = 21.2 eV) spectrum represents the O 2p state
due to the large relative photo-ionization cross-section ofO 2p at low photon energies. Therefore, structures A, B,C, and D in the UPS spectrum are assigned to the Mn 3dO 2p bonding state, the non-bonding O 2p state, the Mn3d t2g plus the Pr 4f states, and the Mn 3d eg state,hν = 930 eV

C'0.65

A'Mn 2 p - 3 d resonancehν = 643.6 eVhν = 600 eVACD0.3

BABhν = 21.2 eV

D0.3C
D x = 0.386420Binding Energy (eV)Fig. 1: Valence band photoemission spectra of Pr1xCaxMnO3. (a) Comparison of spectra taken at various
photon energies; (b) Spectra near EF taken at hν = 21.2eV; (c) hν = 600 eV.
References[1] Y. Tomioka et al., Phys. Rev. B 53, 1689 (1996).
[2] T. Saitoh et al., Phys. Rev. B 51, 13942 (1995).
*ebata@wyvern.phys.s.u-tokyo.ac.jp