Oxygen isotope effect in VO2

Abstract

We investigate the oxygen isotope effect on the ${\mathrm{VO}}_{2}$ metal-insulator transition. Using an alternative method, we synthesize ${\mathrm{V}}^{16}\phantom{\rule{0.16em}{0ex}}{\mathrm{O}}_{2}$ and ${\mathrm{V}}^{18}\phantom{\rule{0.16em}{0ex}}{\mathrm{O}}_{2}$ crystals, finding a 1%--3% phonon softening and a 1.3 K increase in the metal-insulator transition temperature for the latter. A simple calculation, further confirmed by density functional theory, shows that this shift can be attributed to changes in the lattice internal energy. Our results show that lattice dynamics plays a key role in setting the electronic transition temperature, indicating that electronic and structural degrees of freedom remain strongly coupled at the transition.