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

2C/2003G149

Chemical potential shift in Pr1-xCaxMnO3
Kazuaki EBATA*1, Hiroki WADATI1, Masaru TAKIZAWA1, Akira CHIKAMATSU2,
Atsushi FUJIMORI1, Hiroshi KUMIGASHIRA2, Masaharu OSHIMA2,Yasuhide TOMIOKA3, Yoshinori TOKURA3, 4, 5,
1
Department of Complexity Science and Engineering and Department of Physics,
University of Tokyo, Kashiwa, Chiba, 277-8561, Japan2
Department of Applied Chemistry, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
3
Correlated Electron Research Center (CERC),
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8562, Japan
4Department of Applied Physics, 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

106

Users' Reportcore levels, whereas the shift of the Mn 2p core level isdifferent from them because of the additional chemicalshift. Therefore, we consider that the shifts of the O 1s,
Ca 2p and Pr 4d core levels are largely due to ∆µ , andtake the average of the shifts of the three core levels as ameasure of ∆µ in PCMO.
In Fig. 1, we have plotted ∆µ in PCMO thus deduced
as a function of carrier concentration and compared thatin LSMO [6]. For 0.2 ≤ x < 0.3, both ∆µ curves show
similar doping dependences in the sense that the shifts aremonotonous. The differentce between the two is clearlyobserved for x ≥ 0.3, where the CO state occurs in PCMO
but not in LSMO. Therefore, the diffferent chemical
potential shifts in PCMO and LSMO indeed reflect theCO in PCMO, and the µ pinning in the CO state ofPCMO can be understood as due to the electronic “PS”
such as stripe formation.
Chemical potential shift ∆µ (eV)Introduction
Half-doped manganites have been a focus of recent
studies because most of them exhibit a so-called CE-type
antiferromagnetic (AFM) charge-ordered (CO) state. The
compound Pr1-xCaxMnO3 (PCMO) in which thebandwidth W is small in comparison with othermanganites has a particularly stable CO state in the broadhole doping region between x = 0.3 and 0.75. CMR in theCO state of PCMO is remarkable [1]. The origin of theCMR effect has been debated in recent years since it waspointed out that double-exchange interaction alone isinsufficient to explain the large resistivity change withmagnetization [2]. Recently, the possibility of a phaseseparation (PS) scenario as the origin of the CMR effecthas been discussed in theoretical and experimenatal work[3, 4]. In general, electronic “PS” results in the pinning of
the chemical potential µ. Also, electronic “PS” on a nanometer scale, namely stripe formation would lead to thepinning of the chemical potential, in analogy to the caseof high-TC cuprates [5]. The chemical potential shift canbe deduced from the core-level shifts as a function ofcarrier concentrastion by measurements of photoemission
spectroscopy. In this paper, we report on a precise corelevel photoemission study of the chemical potential shift∆µ in single crystals of PCMO as a function of carrier
concentration.
Experimental
Single crystals of PCMO with the carrier
concentrations of x = 0.2, 0.3, 0.45, 0.5 and 0.65 weregrown by the floating-zone method. The photoemission
spectroscopy measurements were performed at BL-2C of
Photon Factory, High Energy Accelerators ResearchOrganization (KEK) using photon energy of hν = 800 eV.
All the measurements were performed under an ultrahighvacuum of ~10-10 Torr at room temperature. Clean
surfaces were obtained by repeated in situ scraping with adiamond file.
Results and Discussion
We have deduced the chemical potential shift ∆µ froma set of core-level shift data. The observed binding energy
shifts with x are common to the O 1s, Ca 2p and Pr 4d

La1-xSrxMnO3
Pr1-xCaxMnO30.1
0-0.1-0.2-0.3
-0.4
00.1

0.2

0.3

0.4

0.5

0.6x, carrier concentration

Fig. 1: Comparison of the chemical potential shift in Pr1xCaxMnO3 with La1-xSrxMnO3 [6].
References[1] Y. Tomioka et al., Phys. Rev. B 53, 1689 (1996).
[2] A. J. Millis et al., Phys. Rev. Lett. 74, 5144 (1995).
[3] A. Moreo et al., Science 283, 2034 (1999).
[4] S. Mori et al., Phys. Rev. Lett. 81, 3972 (1998).
[5] A. Ino et al., Phys. Rev. Lett. 79, 2101 (1997).
[6] J. Matsuno et al., Europhys. Lett. 59, 252 (2002).
* ebata@wyvern.phys.s.u-tokyo.ac.jp