Eur. Phys. J. B 16, 245-250 (2000)
https://doi.org/10.1007/s100510070226

Submillimeter and infrared spectroscopy on La_0.85Sr_0.15MnO₃

¹ LURE, Centre Universitaire Paris-Sud, BP 34, 91898 Orsay Cedex, France
² Experimentalphysik V, Elektronische Korrelationen und Magnetismus, Institut für Physik, Universität Augsburg, 86135 Augsburg, Germany
³ General Physics Institute, Russian Academy of Sciences, 105835 Moscow, Russia
⁴ Moscow Power Engineering Institute, 105835 Moscow, Russia

Received: 5 November 1999
Published online: 15 July 2000

Abstract

The optical conductivity of La_0.85Sr_0.15MnO₃ single crystals was studied by means of submillimeter and infrared spectroscopy for frequencies 4<v<15000 cm^-1 and temperatures 10 K < T < 300 K. The submillimeter conductivity follows the temperature dependence of the dc-data. The phonon spectrum of La_0.85Sr_0.15MnO₃ changes considerably below T_C=180 K revealing a structural phase transition induced by charge or orbital order. At T=10 K a number of phonon modes can be identified in addition to the room-temperature spectrum. The optical conductivity (σ₁) in the mid-infrared reveals the characteristics of small polaron absorption. Below the magnetic ordering temperature the polaron binding energy is highly reduced, but the onset of charge order interrupts the formation of free charge carriers with a Drude-like behavior. The frequency and temperature dependence of σ₁ in this regime qualitatively resembles the small polaron predictions by Millis et al. (Phys. Rev. B 54, 5405 (1996)).