The cooperative Jahn-Teller ordering investigation by absorption spectra in $KDy(MoO_4)_2$

TL;DR

This study investigates the absorption spectra of $KDy(MoO_4)_2$ to understand cooperative Jahn-Teller ordering, revealing temperature-dependent spectral anomalies linked to phase transitions and proposing a phonon mode mechanism for incommensurate phases.

Contribution

It provides new insights into the spectral features and symmetry considerations of Jahn-Teller ordering in $KDy(MoO_4)_2$, highlighting the role of specific phonon modes in phase behavior.

Findings

Spectral anomalies correlate with phase transformations.

Incommensurate phase likely involves coupled $A_u$-type phonons.

Temperature region for incommensurate phase is 17-12 K.

Abstract

Absorption spectra fine structure of $KDy(MoO_4)_2$ in the region of cooperative Jahn-Teller type ordering was studied. Temperature anomalies in the spectra occurring at phase transformation correlate with the ultrasound peculiarities observed earlier. Based on the symmetry approaching, possible activity of the irreducible representations of the rhombic $D_{2h}$ point group was discussed, which lead to the incommensurate phase at cooperative ordering. It was supposed, that coupled $A_u$-type phonon mode may lead to the incommensurate phase existence, which is possible at least in the temperature region 17-12 K.