Abstract
The low-energy excitations of the bilayered manganite have been explored by spectral ellipsometry from two faces of a single crystal over the range from 0.006 to 0.6 eV. This compound is a paramagnetic insulator at ambient temperature, with a transition to a ferromagnetic metal below a Curie temperature of 125 K. Both the -plane and -axis temperature-dependent conductivities have been determined. Essentially no temperature-dependent behavior is observed above although below both the phonon and electronic contributions are strongly temperature sensitive. The highest-frequency phonons, especially those involving Mn-O bond stretching, split and show frequency changes consistent with structural results in the literature, and furthermore there is clear evidence of an increase in electron-phonon coupling at and below . We interpret the temperature-dependent electronic spectral contribution in the light of recent calculations that indicate that a mixed phase exists in the doped manganites below , with coexisting regions of an itinerant large-polaron phase and a localized small-polaron phase.
- Received 17 June 2005
DOI:https://doi.org/10.1103/PhysRevB.72.214437
©2005 American Physical Society