Electronic structure and lattice dynamics of Ba₂CuTeO₆

Yun-Chen Chung^1*, Sunil K. Karna², Fan-Cheng Chou², Hsiang-Lin Liu¹

¹Department of Physics, National Taiwan Normal University, Taipei, Taiwan
²Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan

* Presenter:Yun-Chen Chung, email:coldlizem@gmail.com

We combined spectroscopic ellipsometry and Raman scattering measurements to explore the electronic structure and lattice dynamics in Ba₂CuTeO₆ single crystals. The room temperature optical absorption spectrum of Ba₂CuTeO₆ exhibits four bands at approximately 1.45, 3.43, 4.65 and 5.79 eV. The lowest energy optical absorption was assigned to on-site Cu²⁺ d-d transition. The other higher energy optical absorptions were attributed to charge-transfer transitions between O 2p and Te 5p states. The room temperature Raman scattering spectrum of Ba₂CuTeO₆ shows sixteen phonon modes at approximately 85, 97 104, 118, 160, 194, 380, 196, 404, 409, 492, 568, 574, 606, 678 and 751 cm^-1. With decreasing temperature across 287 K, which is the structural phase transition from monoclinic to triclinic phase, additional phonon modes appear at approximately 124 and 128 cm^-1. Upon further cooling across 75 and 15 K, which are the short-range and long-range antiferromagnetic phase transitions, 124, 128 and 163 cm^-1 phonon modes exhibit a softening, suggesting a coupling between the magnetic and lattice degrees of freedom.

Keywords: strongly correlated electrons, spin-phonon coupling