Raman spectroscopy of the charge- and orbital-ordered state in La0.5Ca0.5MnO3 -: art. no. 144429

被引:57
作者
Abrashev, MV [1 ]
Bäckström, J
Börjesson, L
Pissas, M
Kolev, N
Iliev, MN
机构
[1] Chalmers Univ Technol, Dept Appl Phys, S-41296 Gothenburg, Sweden
[2] Univ Gothenburg, S-41296 Gothenburg, Sweden
[3] NCSR Demokritos, Inst Mat Sci, GR-15310 Athens, Greece
[4] Univ Houston, Texas Ctr Superconduct, Houston, TX 77204 USA
[5] Univ Sofia, Fac Phys, BG-1164 Sofia, Bulgaria
关键词
D O I
10.1103/PhysRevB.64.144429
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
Polarized Raman spectra from microcrystals of La0.5Ca0.5MnO3 were studied as a function of temperature, excitation photon energy, and scattering configuration. At temperatures below the transition from ferromagnetic metallic phase to antiferromagnetic insulating charge- and orbital-ordered (COO) phase, several lines appear in Raman spectra excited with photon energies (h) over bar omega (L)<2.5 eV. We argue that their appearance signals ordering and freezing of the Jahn-Teller distortions at this transition temperature into a superstructure with a doubled elementary cell. We suggest a simplified structural model based on an analysis of the normal phonon modes in the COO phase, neglecting the octahedral tilts and containing ordered Mn4+O6 (undistorted) and Mn3+O6 (Jahn-Teller distorted) octahedra. The symmetries of the experimentally observed Raman lines are determined by comparing their relative intensities to those predicted by the polarization selection rules for a finely twinned quasicubic crystal. The most intensive Raman lines are assigned to definite normal modes in close comparison with corresponding modes in COO layered manganites and undoped RMnO3 (R=La, Y).
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收藏
页码:1444291 / 1444298
页数:8
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