烧绿石XY反铁磁体中稀释诱导的有序
Order Induced by Dilution in Pyrochlore XY Antiferromagnets
摘要：
众所周知，XY烧绿石反铁磁体通过量子和热选择表现出有序无序。在本文中，我们考虑的效果替代非磁性离子的磁性网站烧绿石XY模型一般各向异性交换调整的一个单一的参数$J^{\pm\pm}/J^\pm$。物理学由参数$J^{\pm\pm}/J^\pm=\pm 2$的该空间中的两个点控制，在这两个点处，在基态中存在线模式，并且因此存在介于常规磁体和库仑相位之间的$O(L^2)$基态简并度。在这些点中的每一点处，单个空位产生线缺陷对。两个线缺陷携带不兼容的自旋配置从不同的空位可以交叉导致一个有效的一维描述所产生的自旋织构。在有限密度下的热力学极限中，我们发现稀释选择了一个与从单空位极限中理解的热无序和量子无序所选择的状态“相反”的状态。后一发现暗示了Er $_{2-x}$ Y $_x$ Ti $_2$ O $_7$对小$x$表现出热选择$ψ_2$状态到由淬灭无序选择的$ψ_3$状态的第二相变的可能性。
英文摘要：
XY pyrochlore antiferromagnets are well-known to exhibit order-by-disorder through both quantum and thermal selection. In this paper we consider the effect of substituting non-magnetic ions onto the magnetic sites in a pyrochlore XY model with generally anisotropic exchange tuned by a single parameter $J^{\pm\pm}/J^\pm$. The physics is controlled by two points in this space of parameters $J^{\pm\pm}/J^\pm=\pm 2$ at which there are line modes in the ground state and hence an $O(L^2)$ ground state degeneracy intermediate between that of a conventional magnet and a Coulomb phase. At each of these points, single vacancies seed pairs of line defects. Two line defects carrying incompatible spin configurations from different vacancies can cross leading to an effective one-dimensional description of the resulting spin texture. In the thermodynamic limit at finite density, we find that dilution selects a state "opposite" to the state selected by thermal and quantum disorder which is understood from the single vacancy limit. The latter finding hints at the possibility that Er$_{2-x}$Y$_x$Ti$_2$O$_7$ for small $x$ exhibits a second phase transition within the thermally selected $ψ_2$ state into a $ψ_3$ state selected by the quenched disorder.
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