Zhao Bowen, Takahashi Jun, Sandvik Anders W
Department of Physics, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA.
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Phys Rev Lett. 2020 Dec 18;125(25):257204. doi: 10.1103/PhysRevLett.125.257204.
The S=1/2 square-lattice J-Q model hosts a deconfined quantum phase transition between antiferromagnetic and dimerized (valence-bond solid) ground states. We here study two deformations of this model-a term projecting staggered singlets, as well as a modulation of the J terms forming alternating "staircases" of strong and weak couplings. The first deformation preserves all lattice symmetries. Using quantum Monte Carlo simulations, we show that it nevertheless introduces a second relevant field, likely by producing topological defects. The second deformation induces helical valence-bond order. Thus, we identify the deconfined quantum critical point as a multicritical Lifshitz point-the end point of the helical phase and also the end point of a line of first-order transitions. The helical-antiferromagnetic transitions form a line of generic deconfined quantum-critical points. These findings extend the scope of deconfined quantum criticality and resolve a previously inconsistent critical-exponent bound from the conformal-bootstrap method.
S = 1/2 正方晶格J - Q模型存在反铁磁基态和二聚化（价键固体）基态之间的无约束量子相变。我们在此研究该模型的两种变形——一个投影交错单重态的项，以及对形成强弱耦合交替“阶梯”的J项的调制。第一种变形保持所有晶格对称性。通过量子蒙特卡罗模拟，我们表明它仍然引入了第二个相关场，可能是通过产生拓扑缺陷。第二种变形诱导螺旋价键序。因此，我们将无约束量子临界点识别为一个多临界里夫希茨点——螺旋相的终点以及一阶转变线的终点。螺旋 - 反铁磁转变形成一条一般的无约束量子临界点线。这些发现扩展了无约束量子临界性的范围，并解决了之前共形引导法中不一致的临界指数界限问题。
