Quantum Versus Jahn-Teller Orbital Physics in ${\mathrm{Y}\mathrm{V}\mathrm{O}}_3$ and ${\mathrm{L}\mathrm{a}\mathrm{V}\mathrm{O}}_3$

We argue that the large Jahn-Teller (JT) distortions in ${\mathrm{Y}\mathrm{V}\mathrm{O}}_3$ and ${\mathrm{L}\mathrm{a}\mathrm{V}\mathrm{O}}_3$ should suppress the quantum orbital fluctuation. The unusual magnetic properties can be well explained based on local density approximation $+$ Hubbard U calculations using experimental structures, in terms of the JT orbital. The observed splitting of the spin-wave dispersions for ${\mathrm{Y}\mathrm{V}\mathrm{O}}_3$ in a $C$-type antiferromagnetic state is attributed to the inequivalent ${\mathrm{V}\mathrm{O}}_2$ layers in the crystal structure, instead of the “orbital-Peierls state.” Alternative stacking of $ab$-plane exchange couplings produces the $c$-axis spin-wave splitting; thus, the spin system is highly three dimensional rather than quasi-one-dimensional. Similar splitting is also predicted for ${\mathrm{L}\mathrm{a}\mathrm{V}\mathrm{O}}_3$, although it is weak.

Figure 1

The calculated $t_{2g}$ orbital occupation numbers for different compounds as a function of different magnetic orderings. Since the OO patterns are fixed by the structures, only the occupations for one of the transition-metal sites are shown.

Figure 2

The calculated spin-wave dispersions for various compounds in the Heisenberg model. Solid lines are results using calculated exchange coupling constants, while dotted lines are that using the single average of two $J_{ab}$.