Role of strong electronic correlations in the metal-to-insulator transition in disordered LiAlyTi2-yO4

The compound LiAlyTi2-yO4 undergoes a metal-to-insulator transition for yc approximately 0.33. It is known that disorder alone is insufficient to explain this transition; e.g., a quantum site percolation model predicts yc approximately 0.8. We have included (Hubbard) electronic interactions into a model of this compound, using a real-space Hartree-Fock approach that achieves self-consistency at every site, and have found that for a Hubbard energy equal to 1.5 times the non-interacting bandwidth one obtains yc approximately 0.3. Further, with increasing Hubbard energy we find an Altshuler-Aronov suppression of the density of states, deltaN(epsilon) approximately square root /epsilon-epsilonF/, that reduces the density of states at the Fermi energy to zero at the critical Hubbard interaction. Using this ratio of correlation to hopping energy one is led to a prediction of the near-neighbor superexchange (J/t approximately 1/3) which is similar to that for the cuprate superconductors.