Effect of correlations and disorder on electron states in the Mott-Hubbard insulator ${\mathrm{V}}_2$${\mathrm{O}}_3$

We compare vanadium-deficient (nonstoichiometric) and titanium-doped vanadium sesquioxide through measurements of the electrical resistivity at a series of hydrostatic pressures, the magnetic susceptibility, and the low-temperature specific heat: all as a function of T. The pressure dependence of the critical temperature for the discontinuous metal-antiferromagnetic-insulator transition as well as the temperature dependence of the magnetic susceptibility track in the two cases. However, the pressure dependence of the Hubbard gap, the slower than exponential form of the low-temperature resistivity, and the concentration of two-level systems are markedly different for ${\mathrm{V}}_{1.9967}$${\mathrm{O}}_3$ and (${\mathrm{V}}_{0.99}$${\mathrm{Ti}}_{0.01}$${)}_2$${\mathrm{O}}_3$. We discuss our results in terms of the intra-atomic Coulomb repulsion, which is of comparable magnitude to the bare bandwidth of the vanadium 3d states. The band splitting in the antiferromagnetic insulating state is argued to cross over to a Slater-type splitting between the subbands narrowed by correlations with a sufficient degree of oxygen nonstoichiometry or Ti doping.