Vanadium Dioxide: A Peierls-Mott Insulator Stable against Disorder

Vanadium dioxide undergoes a first order metal-insulator transition at 340 K. In this Letter, we develop and carry out state-of-the-art linear scaling density-functional theory calculations refined with nonlocal dynamical mean-field theory. We identify a complex mechanism, a Peierls-assisted orbital selection Mott instability, which is responsible for the insulating $M_1$ phase, and which furthermore survives a moderate degree of disorder.

Figure 1

Dependence of the spectral function $\rho (\omega )$ with respect to the Coulomb repulsion $U_d$.

Figure 2

(a) Spectral function $\rho$ of paramagnetic ${\mathrm{VO}}_2$ in the presence of Gaussian disorder $\delta$. (b) Averaged quasiparticle weight $Z_d$ with respect to the repulsion $U_d$ for zero ($\delta =0\AA$) to large disorder ($\delta =0.5\AA$). Calculations including a single O vacancy in the $\delta =0\AA$ case are also shown for comparison (open squares). (c) Distribution of the local quasiparticle weight $Z_{d,i}$ for $\delta =0.1\AA$. (d) Isosurface of the real space representation of the Fermi density for disorder $\delta =0.3\AA$. The large (small) sphere denotes V (O) atoms along the rutile axis.

Figure 3

(a) Spectral function $\rho$ obtained using cellular cluster DMFT (c-DMFT) calculations without ($\delta =0\AA$) disorder for moderate (324 atom) and large (768 atom) supercells. Calculations for disordered ${\mathrm{VO}}_2$ ($\delta =0.1\AA$) and for a single O vacancy are also shown for comparison. Inset: Enlargement of the low energy scale, the gap of $\sim 0.6\mathrm{eV}$ is shown. The vacancy introduces a midgap state, highlighted by the arrow. (b) Isosurface of the real space representation of the charge density at the Fermi level for calculations for an O vacancy (star). The large (small) sphere denotes V (O) atoms along the rutile axis (horizontal direction). (c) Imaginary part of the self-energy and (inset) imaginary part of the Green’s function for $\delta =0\AA$.

Figure 4

(a) Theoretical optical conductivity along the rutile axis (solid lines) and along the perpendicular direction (dashed lines) calculated with cellular DMFT. Experimental (exp.) data for polycrystalline films [27] (squares) and thin films (diamonds) [28] are shown for comparison. (b) Optical conductivity along the rutile axis obtained by cellular DMFT for disordered ${\mathrm{VO}}_2$ for various disorder amplitudes $\delta$.