Department of Physics, University of California, Davis, Davis, California 95616, USA.
Phys Rev Lett. 2012 Jul 13;109(2):026404. doi: 10.1103/PhysRevLett.109.026404.
We investigate ground state properties of the half-filled staggered-flux Hubbard model on a square lattice. Energy gaps to charge and spin excitations and magnetic as well as dimer orders are calculated as a function of interaction strength U/t by means of a constrained-path quantum Monte Carlo method. It is found that the system is a semimetal at U/t≲5.6 and a Mott insulator, with long-range antiferromagnetic order, at U/t≳6.6. In the range 5.6≲U/t≲6.6, the ground state is a correlated insulator where both magnetic and dimer orders are absent. Furthermore, spin excitation in the intermediate phase appears to be gapless, and the measured spin-spin correlation function exhibits power-law decaying behavior. The data suggest that the nonmagnetic ground state is a possible candidate for the putative algebraic spin liquid.
我们研究了正方晶格上半填满交错磁通 Hubbard 模型的基态性质。通过受限路径量子蒙特卡罗方法，计算了电荷和自旋激发、磁有序和二聚体有序的能隙作为相互作用强度 U/t 的函数。结果发现，当 U/t≲5.6 时，系统为半金属，当 U/t≳6.6 时，系统为莫特绝缘体，具有长程反铁磁序。在 5.6≲U/t≲6.6 的范围内，基态为关联绝缘态，不存在磁有序和二聚体有序。此外，中间相中的自旋激发似乎是无能隙的，测量得到的自旋-自旋相关函数呈现出幂律衰减行为。这些数据表明，非磁性基态可能是假设的代数自旋液体的候选物。
