Studies on strongly correlated electron systems

The Anderson lattice model and the Heisenberg model are investigated by exact numerical calculations and renormalization group method. First, we show exactly that the ground state of the Anderson lattice with U=∞ is ferromagnetic for Ne=N+1 if the level of localized electrons Εf is deep enough. This indicates that a transition to a magnetically ordered state will occur for a value of Εf less than a critical value Εfc. Second, we study the low-temperature behavior of quantum antiferromagnets in two -space dimensions. The renormalization group theory predicts an order -disorder transition at finite hole concentration δc.