Quantum non-magnetic state near metal-insulator transition-A possible candidate of spin liquid state

In this paper, based on the formulation of an O(3) non-linear sigma model, we study the two-dimensional pi-flux Hubbard model at half-filling. A quantum non-magnetic insulator is explored near the metal-insulator transition that may be a possible candidate of the spin liquid state. Such quantum non-magnetic insulator on square lattice is not induced by frustrations. Instead, it originates from quantum spin fluctuations with relatively small effective spin moments. In the strong-coupling limit, our results of the spin velocity and spin order parameter agree with results obtained from earlier calculations. Copyright (C) EPLA, 2009