Terahertz–infrared electrodynamics of overdoped manganites La_1–xCa_xMnO₃

Abstract

We have measured low-temperature terahertz and infrared spectra of La_1–xCa _xMnO₃ with x = 0.5; 0.6; 2/3, 0.7; 3/4, 0.85; 0.9; 0.95; 0.98 and x = 1 in the form of ceramics and epitaxial films. In the charge-ordered state for commensurate dopings (x = 2/3 and 3/4), we observed an absorption band at frequencies corresponding to the position of the lowest energy van Hove singularity in the folded Brillouin zone. The band is assigned to the boson peak. We observed qualitatively the same boson peak in Raman spectra of La_1/3Ca_2/3MnO₃ ceramics. In antiferromagnetic phase, for the 0.5 ≤ x < 0.85 range of doping, the conductivity mechanism gradually changes from a hopping-like transport at low temperatures to the Drude behavior at elevated temperatures in the paramagnetic phase. For 0.85 ≤ x < 1 (canted antiferromagnetic phase), the electrons behave as Drude-like carriers in the whole temperature interval 5–300 K.

Keywords:

• manganites
• terahertz

Acknowledgments

The research was supported by the Russian Ministry of Education and Science (Program ‘5top100’), the Russian Foundation for Basic Research [13-02-12416] and the Czech Science Foundation (Project No. P204/12/1163).

Additional information

Funding

We acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG) [grant number DR228/36].