We study phase transitions of coupled two dimensional XY systems with spatial anisotropy and $U(1) \times \mathbb{Z}_2$ symmetry, motivated by spinless bosonic atoms trapped in square optical lattice on the metastable first excited $p-$level orbitals with anisotropic hopping amplitudes. The phase transitions of the system are generally split into an Ising transition and an XY transition, but the sequence and the nature of the transitions depend on the ratio between the anisotropic couplings. In the isotropic limit the XY variables are expected to be disordered before the Ising variables when thermal or quantum fluctuations are turned on gradually. In the anisotropic limit with zero perpendicular hoppings, the finite temperature transition is a Kosterlitz-Thouless transition driven by proliferation of hybrid half vortices, and the zero temperature quantum phase transition is split into a bond order transition and a 3D XY transition, which can be driven by the condensation of either single vortices or half vortices. After the condensation of half vortices the resultant state is a Mott Insulator of paired bosons. A small perpendicular hopping $J_b$ leads to a 2D Ising transition at low temperature and a 2+1d quantum Ising transition with a small charging energy at zero temperature. Global phase diagrams for both classical and quantum phase transitions are drawn. The analytical results obtained in this work are expected to be checked both numerically and experimentally.
Spin transport in the Neel and collinear antiferromagnetic phase of the two dimensional spatial and spin anisotropic Heisenberg model on a square lattice
Non-equilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar coupled spin-glass LiHo$_{0.5}$Er$_{0.5}$F$_{4}$
我们提出了一个研究模型自旋玻璃LiHo $_{0.5}$ Er $_{0.5}$ F $_4$同时使用交流磁化率，磁化强度和磁热效应测量以及小角中子散射（SANS）在亚开尔文温度。所有测得的批量揭示滞后行为时，沿晶体学c轴施加的字段。此外，雪崩般的松弛后，从零场冷却状态斜坡到$200 - 300$ Oe的静态字段中观察到。SANS测量被用来跟踪整个磁滞回线和相关的松弛微观自旋重构。将SANS数据与在一百万个晶胞的盒子上进行的非均匀平均场计算进行比较，提供了自旋组态的真实空间图像。我们发现雪崩是由释放的塞曼能量驱动的，塞曼能量加热样品并产生正反馈，继续雪崩。SANS和平均场模拟的组合表明，传统的集群大小的分布被一个中间集群大小耗尽的磁滞回线。
Giant Magnetocrystalline Anisotropy in Honeycomb Iridate NiIrO3 with Large Coercive Field Exceeding 17 T
School of Chemistry, Sun Yat-Sen University（中山大学化学学院）；School of Chemistry and Environment, Jiaying University（嘉应学院化学与环境学院）；School of Physics, Sun Yat-Sen University（中山大学物理学院）；School of Physics, Huazhong University of Science and Technology（华中科技大学物理学院）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；School of Chemistry and Chemical Engineering, Hainan University（海南大学化学化工学院）
Effect of the Canting of Local Anisotropy Axes on Ground-State Properties of a Ferrimagnetic Chain with Regularly Alternating Ising and Heisenberg Spins
