Low-Energy Excitations in La1.2Sr1.8Mn2O7 Investigated by Ellipsometry
The low-energy excitations of the bilayered manganite La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} 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 (T{sub c}) of 125 K. Both the ab-plane and c-axis temperature-dependent conductivities have been determined. Essentially no temperature-dependent behavior is observed above T{sub c} although below T{sub c} 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 Tc. 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 T{sub c}, with coexisting regions of an itinerant large-polaron phase and a localized small-polaron phase.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States). National Synchrotron Light Source
- Sponsoring Organization:
- Doe - Office Of Science
- DOE Contract Number:
- DE-AC02-98CH10886
- OSTI ID:
- 913661
- Report Number(s):
- BNL-78229-2007-JA; PRBMDO; TRN: US0801364
- Journal Information:
- Phys. Rev. B, Vol. 72; ISSN 0163-1829
- Country of Publication:
- United States
- Language:
- English
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