paper

Orbital Dimerization and Dynamic Jahn-Teller Effect in NaTiSi $_{2}$ O $_{6}$

arXiv:cond-mat/0210191

Abstract

We study with the Raman scattering technique two types of phase transitions in the pyroxene compounds NaMSi $_{2}$ O $_{6}$ (with M=Ti, V, and Cr). In the quasi one-dimensional S=1/2 system NaTiSi $_{2}$ O $_{6}$ we observe anomalous high-temperature phonon broadening and large changes of the phonon energies and line-widths across the phase transition at 210 K. The phonon anomalies originate from an orbital order-disorder phase transition and these results --combined with theoretical considerations-- indicate that the high temperature dynamical Jahn-Teller phase of NaTiSi $_{2}$ O $_{6}$ exhibits a spontaneous breaking of translational symmetry into a dimerized, Jahn-Teller distorted, orbital ordered state under the formation of spin valence bonds. In S=1 NaVSi $_{2}$ O $_{6}$ orbital degrees of freedom are strongly suppressed and the magnetic excitations are well described within a Heisenberg model, indicating that at T $_{N}$ =19K this system orders antiferromagnetically.

4 pages, 4 figures embedded

Orbital Dimerization and Dynamic Jahn-Teller Effect in NaTiSi2​O6​

Abstract

Orbital Dimerization and Dynamic Jahn-Teller Effect in NaTiSi $_{2}$ O $_{6}$