Optical response of ferromagnetic YTiO₃ studied by spectral ellipsometry

Kovaleva, N. N.; Boris, A. V.; Yordanov, P.; Maljuk, A.; Brücher, E.; Strempfer, J.; Konuma, M.; Zegkinoglou, I.; Bernhard, Christian; Stoneham, A. M.; Keimer, B.

doi:10.1103/PhysRevB.76.155125

Back

Journal article

Optical response of ferromagnetic YTiO₃ studied by spectral ellipsometry

Kovaleva, N. N. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Boris, A. V. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Yordanov, P. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Maljuk, A. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Brücher, E. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Strempfer, J. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Konuma, M. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Zegkinoglou, I. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
Bernhard, Christian Department of Physics, University of Fribourg, Switzerland
Stoneham, A. M. Department of Physics and Astronomy, University College London, United Kingdom
Keimer, B. Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany

26.10.2007

Published in:

Physical Review B: Condensend Matter and Materials Physics. - 2007, vol. 76, no. 15, p. 155125

English We have studied the temperature dependence of spectroscopic ellipsometry spectra of an electrically insulating, nearly stoichiometric YTiO₃ single crystal with ferromagnetic Curie temperature T_C=30 K. The optical response exhibits a weak but noticeable anisotropy. Using a classical dispersion analysis, we identify three low-energy optical bands at 2.0, 2.9, and 3.7 eV. Although the optical conductivity spectra are only weakly temperature dependent below 300 K, we are able to distinguish high- and low-temperature regimes with a distinct crossover point around 100 K. The low-temperature regime in the optical response coincides with the temperature range in which significant deviations from a Curie-Weiss mean-field behavior are observed in the magnetization. Using an analysis based on a simple superexchange model, the spectral weight rearrangement can be attributed to intersite d _i¹d _j¹→d _i² d _j⁰ optical transitions. In particular, Kramers-Kronig consistent changes in optical spectra around 2.9 eV can be associated with the high-spin-state (³T₁) optical transition. This indicates that other mechanisms, such as weakly dipole-allowed p-d transitions and/or exciton-polaron excitations, can contribute significantly to the optical band at 2 eV. The recorded optical spectral weight gain of the 2.9 eV optical band is significantly suppressed and anisotropic, which we associate with complex spin-orbit-lattice phenomena near the ferromagnetic ordering temperature in YTiO₃.

Faculty

Faculté des sciences et de médecine

Department

Département de Physique

Language