Koga A, Kawakami N
Department of Applied Physics, Osaka University, Suita, Osaka 565-0871, Japan.
Phys Rev Lett. 2000 May 8;84(19):4461-4. doi: 10.1103/PhysRevLett.84.4461.
We investigate quantum phase transitions in the frustrated antiferromagnetic Heisenberg model for SrCu2(BO3)(2) by using the series expansion method. It is found that a novel spin-gap phase, adiabatically connected to the plaquette-singlet phase, exists between the dimer and the magnetically ordered phases known thus far. When the ratio of the competing exchange couplings alpha( = J'/J) is varied, this spin-gap phase exhibits a first- (second-) order quantum phase transition to the dimer (the magnetically ordered) phase at the critical point alpha(c1) = 0.677(2) [ alpha(c2) = 0. 86(1)]. Our results shed light on some controversial arguments about the nature of quantum phase transitions in this model.
我们使用级数展开方法研究了SrCu2(BO3)2的受挫反铁磁海森堡模型中的量子相变。结果发现，在迄今已知的二聚体相和磁有序相之间存在一个与面元单重态相绝热相连的新型自旋能隙相。当竞争交换耦合比α(= J'/J)变化时，这个自旋能隙相在临界点α(c1)=0.677(2)[α(c2)=0.86(1)]处表现出向二聚体（磁有序）相的一级（二级）量子相变。我们的结果为关于该模型中量子相变本质的一些有争议的观点提供了线索。
