Structural and electronic phase transition in a
metal-insulator manganite superlattice
M. Nakamura,1 D. Okuyama,1 J. S. Lee,2 T. Arima,3 Y. Wakabayashi,4R. Kumai,5 M. Kawasaki,1,6 and Y. Tokura1,3,7
1

Cross-Correlated Materials Research Group (CMRG) and Correlated Electron
Research Group (CERG), ASI, RIKEN, Wako, 351-0198, Japan
2
Multiferroic Project, Exploratory Research for Advanced Technology (ERATO),
Japan Science and Technology Agency (JST), Japan
3
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
Japan
4Division of Materials Physics, Graduate School of Engineering Science, OsakaUniversity, Japan
5
National Institute of Advanced Industrial Science and Technology (AIST), Japan
6
WPI-Advanced Institute for Materials Research (AIMS), Tohoku University, Japan
7
Department of Applied Physics, University of Tokyo, Japan
Phase competition between the ferromagnetic-metallic (FM-M) state and thecharge/orbital ordered insulating (COO-I) state is an essential ingredient of the colossal
magnetoresistance in perovskite manganites. Recently it was found that these twocontrastive phases can be reproduced even in the thin-film form by using (011) surfaceof perovskite substrates [1][2]. This finding opened up the thin-film-specific new
approaches to the control of the phase competition, such as the anisotropic stress
imposed by the epitaxial strain [3][4], combinatorial method [5] and artificial
superstructures [6]. Here we demonstrated that the superstructures composed ofnanoscale FM-M and COO-I layers can be a novel host of the phase competing state[6].
A superlattice composed of 5 layer La0.5Sr0.5MnO3 (FM-M) and 5 layer
Pr0.5Ca0.5MnO3 (COO-I) was grown on LSAT(011) substrate. The superlattice firstbecame FM-M at 240 K and succesively turned into the COO-I state at 180 K with alarge thermal hysteresis, supporting the senario of phase coexistence and theircompetition in the superlattice. We further confirmed the existence of both COO-I andFM-M phases by synchrotron X-ray diffraction and infra-red (IR) optical conductivity.
The synchrotron X-ray diffraction clarified the 4-fold periodicity associated with thecharge/orbital ordering, while the IR optical conductivity showed a gap-less featureeven in the insulating ground state. These results indicate that the two phases arecoexisting in the superlattice and the phase domain boundaries are locating near thechemical composition boundaries.
Magnetic-field dependence of the resistivity and magnetization after field coolingshows a relaxor-like behavior. This indicates that the phase domain boundaries arestable at low temperatures and their positions are tunable by a magnetic field.
[1] M. Nakamura et al., Appl. Phys. Lett. 86, 182504 (2005).
[2] Y. Ogimoto et al., Phys. Rev. B 71, 060403(R) (2005).
[3] D. Okuyama et al., Appl. Phys. Lett., 95, 152502 (2009) .
[4] K. Lai and M. N. et al., Science 329, 190 (2010).
[5] J. S. Lee et al. Phys. Rev. B 82, 052406 (2010).
[6] M. Nakamura et al., Adv. Mater. 22, 500 (2010).
This research is supported by the Japan Society for the Promotion of Science (JSPS) through its“Funding Program for World-Leading Innovative R&D on Science and Technology (FIRSTProgram).