Optical Study of the Electronic Structure and Lattice Dynamics of YBaMn2O6 Single Crystals

Rea Divina Mero^1*, Hsiang-Lin Liu¹, Shigeki Yamada²

¹Physics, National Taiwan Normal University, Taipei 11677, Taiwan
²Department of Material System Science, Yokohama City University, Yokohama 236-0027, Japan

* Presenter:Rea Divina Mero, email:readivina@gmail.com

We investigated the electronic structure and lattice dynamics of double perovskite YBaMn2O6 single crystals through spectroscopic ellipsometry and Raman scattering spectroscopy. This material is interesting because it exhibits complex structural, magnetic and charge/orbital ordering phase transitions. Room temperature optical absorption spectrum of YBaMn2O6 shows three bands around 1.50, 4.05, and 5.49 eV. The lowest optical absorption band centered at approximately 1.50 eV was assigned to on-site d–d transitions in Mn, whereas the optical features at approximately 4.05 and 5.49 eV were assigned to charge-transfer transitions between the 2p state of O and 3d state of Mn. Room temperature Raman scattering spectrum shows eighteen phonon modes at approximately 134, 142, 161, 181, 210, 249, 265, 301, 333, 345, 370, 386, 414, 435, 470, 496, 513, 618 and 644 cm-1. Phonon modes below 300 cm-1 involve the motion of Y and Ba atoms. Phonon modes between 300 and 400 cm-1 are due to mix vibrations of stretching, bending, and tilting. The strong phonon peaks at 496 and 513 cm-1 are mainly due to Jahn-Teller stretching while the peaks at 610 and 644 cm-1 are assigned to the breathing modes of the oxygen atoms in the MnO6 octahedra. With decreasing temperature, these phonon modes show a shift of peak position to higher frequencies and a narrowing of the resonance linewidth. Notably, new phonon modes appear in the spectra range between 200 and 400 cm-1 below 200 K which can be associated to charge ordering. Furthermore, magnetic order-induced changes were observed in the breathing modes with the splitting of the 618 cm-1 and a very large enhancement of the 644 cm-1 peak. Anomalies in the phonon frequency and linewidth observed near the phase transition temperatures highlight the importance of charge–orbital–spin interactions in this material.

Keywords: double perovskite, strongly correlated electrons, charge-ordering, Jahn-Teller stretching