Trimerization and orbital ordering in Ba1−xSrxV13O18

Abstract

We studied the physical properties of ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{V}}_{13}{\mathrm{O}}_{18}$ single crystals, which exhibit three different phases caused by the orbital and charge degrees of freedom in V ${t}_{2g}$ states. We found from the magnetic susceptibility and the NMR measurement that the low-temperature phase of this series of compounds is characterized by the spin-singlet state. We also found from the electrical resistivity and optical conductivity spectra that these compounds become heavily anisotropic in the low-temperature phase with V trimerization, indicating that the orbital ordering of V ${t}_{2g}$ states causes the anisotropy of the electronic structure of this series of compounds.