Quantum Phase Transitions in the Shastry-Sutherland Model for SrCu 2 \(BO 3 \) 2

摘要: We investigate quantum phase transitions in the frustrated antiferromagnetic Heisenberg model for SrCu2(BO3)(2) by using series expansion method. It is found that a novel spin-gap phase, adiabatically connected to plaquette-singlet exists between dimer and magnetically ordered phases known thus far. When ratio of competing exchange couplings alpha( = J'/J) varied, this exhibits first- (second-) order transition (the ordered) at critical point alpha(c1) 0.677(2) [ alpha(c2) 0. 86(1)]. Our results shed light on some controversial arguments about nature model.