Impurity induced insulator-to-metal transitions in half-filled Mott insulators

In view of cuprate superconductors, effects of point-type impurity potential ( V ) on half-filled antiferromagnetic and paramagnetic states are studied for a strongly correlated square-lattice Hubbard model ( U / t = 12) with a diagonal transfer ( t ′), using a variational Monte Carlo method. In the trial states, we introduce a Rice-Brinkman-type one-body projector for V , which enables us to treat the whole range of V (− ∞ < V / t < ∞) with small statistical errors. Filling-control-type Mott (insulator-to-metal) transitions are found to occur at V = V U ( ± ) (∼ ± U ). In the metallic states \left| V_{U}^{\left( \pm \right)} \right| \right)$?> ( | V | > | V U ( ± ) | ) , charge carriers are holes (electrons) in the case of attractive (repulsive) potential. The mechanism of the transitions is intuitively understood.