File(s) under permanent embargo

Reason: This item is currently closed access.

Low-energy Mott-Hubbard excitations in LaMnO3 probed by optical ellipsometry

journal contribution
posted on 24.11.2014, 17:00 by Natalia Kovaleva, Andrzej M. Oles, A.M. Balbashov, A. Maljuk, D.N. Argyriou, G. Khaliullin, B. Keimer
We present a comprehensive ellipsometric study of an untwinned, nearly stoichiometric LaMnO 3 crystal in the spectral range 1.2–6.0 eV at temperatures 20≤T≤300 K . The complex dielectric response along b and c axes of the Pbnm orthorhombic unit cell, ε ̃ b (ν) and ε ̃ c (ν) , is highly anisotropic over the spectral range covered in the experiment. The difference between ε ̃ b (ν) and ε ̃ c (ν) increases with decreasing temperature, and the gradual evolution observed in the paramagnetic state is strongly enhanced by the onset of A -type antiferromagnetic long-range order at T N =139.6 K . In this study we focus on the analysis of excitations observed at high energy (∼4–5 eV) and show that the observed temperature changes of their spectral weight are opposite to those found for the lowest-energy gap excitation at ∼2 eV . We used a classical dispersion analysis to quantitatively determine the temperature-dependent optical spectral-weights shifts between low- and high-energy optical bands. Based on the observation of a pronounced spectral-weight transfer between both features upon magnetic ordering, they are assigned to high-spin and low-spin intersite d 4 d 4 ⇌d 3 d 5 transitions by Mn electrons. The anisotropy of the lowest-energy optical band and the spectral-weight shifts induced by antiferromagnetic spin correlations are quantitatively described by an effective spin-orbital superexchange model. An analysis of the multiplet structure of the intersite transitions by Mn e g electrons allowed us to estimate the effective intra-atomic Coulomb interaction, the Hund exchange coupling, and the Jahn-Teller splitting energy between e g orbitals in LaMnO 3 , as well as to extract experimental information concerning the type of orbital order in LaMnO 3 . This study identifies the lowest-energy optical transition at ∼2 eV as an intersite d-d transition whose energy is substantially reduced compared to that obtained from the bare intra-atomic Coulomb interaction.

Funding

A.M.O. acknowledges financial support by the Foundation for Polish Science FNP and by the Polish Ministry of Science and Higher Education under Project No. N202 068 32/1481.

History

School

  • Science

Department

  • Physics

Published in

PHYSICAL REVIEW B

Volume

81

Issue

23

Pages

? - ? (13)

Citation

KOVALEVA, N.N. ... [et al.], 2010. Low-energy Mott-Hubbard excitations in LaMnO3 probed by optical ellipsometry. Physical Review B, 81, no. 235130.

Publisher

© American Physical Society

Version

AM (Accepted Manuscript)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/

Publication date

2010

ISSN

1098-0121

eISSN

1550-235X

Language

en