Charge modulation in a one-dimensional orbital chain
in electron-doped cubic SrMnO3
H. Sakai1, D. Okuyama1, H. Nakao2, Y. Murakami2, K. Sugimoto3, T. Arima3,4,
Y. Taguchi1, and Y. Tokura1,5,61

CMRG-CERG, RIKEN-ASI, Wako 351-0198, Japan
CMRC-PF, IMSS, KEK, Tsukuba, 305-0801, Japan
3RIKEN SPring-8 Center, Hyogo 679-5198, Japan
4IMRAM, Tohoku Univ., Sendai 980-8577, Japan
5Department of Applied Physics, Univ. of Tokyo, Tokyo 113-8656, Japan
6Multiferroics Project, ERATO, JST, Tokyo 113-8656, Japan2Charge- and orbital-ordering phenomena observed in strongly correlated electronsystems have long attracted significant interest, since they often govern the physicalproperties of the systems, such as transport, optical and dielectric responses. Typicalexamples are the hole-doped perovskite-type manganites R1-xAxMnO3 (R and A beingrare-earth and alkaline-earth ions, respectively). Around 50% hole doping, in particular,
the charge ordering accompanied by the ordering of d3x2-r2/d3y2-r2-type eg orbitals showsup, which has been intensively investigated so far in terms of the colossal
magnetoresistance phenomena. With increasing the hole concentration, the pattern ofthe charge, orbital and spin ordering successively changes, and finally there appears theone-dimensional d3z2-r2-type orbital ordering with the C-type (interchain)
antiferromagnetism (inset to Fig. 1) for ~80% hole doping. In a further hole-doped
regime (i.e. the electron-doped A2+Mn4+O3 systems), however, the electronic phase
diagram has been still unclear due to the difficulty in synthesizing single crystals.
We have recently developed a new synthesis technique combining the floating-zone
and the high-pressure method, and succeeded in obtaining the single crystals of cubic
SrMnO3 and its electron-doped analogues. Figure 1 shows an electronic phase diagramfor Sr1-xCexMnO3 below 20% electron doping. Surprisingly, electrons with as low
concentration as 4% make the ground state d3z2-r2-orbital-ordered insulating phase,
while the metallic phase is strongly suppressed (only below 2%). In this study, we haveinvestigated in detail the electronic and lattice properties of such self-organized dilutepolarons by performing the single-crystal x-ray diffraction at BL4C, KEK-PF.
Figures 2 show the diffraction patterns around the 115 reflection (in the pseudo cubicsetting) for the x=0.05 compound. Below the orbital-ordering temperature (~190 K),
the Bragg spot splits into two due to a minor twin domain in the tetragonal phase. Withfurther decreasing the temperature, the diffuse scattering along ( 0 ) and (0  )
gradually evolves and results in a broad peak structure with ~0.08-0.09 at the lowest
temperature. This suggests the (short-range) ordering of the carriers (~10%) doped in
the d3z2-r2 orbital chains. The difference in temperature dependence of theorder parameters between the charge and orbital sectors was clearlyobserved.
Sr1-xCexMnO3 (x=0.05), 115 reflection

Sr1-xCe(4+)xMnO3
G-AFM
300 insulator

T (K)

200

100

TN (G)PM metalTOO

TN (C)

10 K

175 K

230 K

5.1

L 5.0

G
AFM
metal
TCA

00

5.2

4.9

C-AFM orbital-orderedinsulator

0.1
0.2
2x (electron concentration)

Fig. 1: Electronic phase diagramfor Sr1-xCexMnO3 as a functionof electron concentration (2x).

4.8
0.8

0.9

1.0

1.1

0.8
1.2

0.9

1.0

1.1

0.8

0.9

1.0

1.1

HHHFig. 2: Contour plots of the diffuse scattering around the (115) Braggreflection on the (H 1 L) plane at 10, 175, and 230 K. The indices are basedon the (pseudo) cubic setting.