论文标题
磁场三角形晶格上的自旋1/2抗铁磁铁的异常动力学
Unusual dynamics of spin-1/2 antiferromagnets on the triangular lattice in magnetic field
论文作者
论文摘要
从理论上讲，我们在磁场$ \ bf h $中的三角晶格上讨论了旋转1/2海森贝格抗铁磁铁的动力学特性。我们使用最近提出的键合理论，该理论用包含三个自旋的整个磁性单位电池的量子状态运行。该技术描述了准确的短距离自旋相关性，并提供了基本激发的定量描述，这些激发出现在其他方法中，作为传统低能量准粒子的结合状态（例如，镁质）。在与先前的数值和分析结果的定量一致性中，我们观察到具有共面旋转排列的四个阶段在磁场上增加：三个共同的Y期，共线“上下”（UUD）状态（UUD）状态，非差异V型相位，非差异V型相，以及共线完全极化（FP）。我们证明，除了镁质外，在UUD状态下还存在Spin-0基本激发，其中一个长期存在，其频谱位于镁分支以下。该模式起源于$ h = 0 $的高能准粒子，仅在纵向自旋相关器中产生异常。在V期中，我们获得了多个短波旋转激发，这些激发在半经典的自旋理论中没有对应物。我们通过非共线V型相（将纵向和横向通道混合在一起），在从一个共线状态（UUD）到另一个（FP）的途中证明了准颗粒光谱的高度非平底场演化。特别是，在UUD状态下的Spin-0分支的某些部分变成了FP相中的Spin-1（Magnon）分支的一部分，而一个磁杆分支的某些部分变成了Spin-2分支的一部分。通过任何常规的分析方法，这种进化将很难找到。我们的结果与最近以$ \ rm ba_3cosb_2o_9 $，$ \ rm kybse_2 $和$ \ rm csybse_2 $获得的中子实验数据非常吻合。
We theoretically discuss dynamical properties of spin-1/2 Heisenberg antiferromagnet on the triangular lattice in magnetic field $\bf H$. We use the recently proposed bond-operator theory which operates with quantum states of the whole magnetic unit cell containing three spins. This technique describes accurately short-range spin correlations and provides a quantitative description of elementary excitations which appear in other approaches as bound states of conventional low-energy quasiparticles (e.g., magnons). In quantitative agreement with previous numerical and analytical findings, we observe four phases with coplanar spin arrangements upon the field increasing: the three-sublattice Y-phase, the collinear "up-up-down" (UUD) state, the non-collinear V-phase, and the collinear fully polarized (FP) state. We demonstrate that apart from magnons there are spin-0 elementary excitations in the UUD state one of which is long lived and its spectrum lies below magnon branches. This mode originates from a high-energy quasiparticle at $H=0$ and it produces anomalies only in the longitudinal spin correlator. In the V-phase, we obtain multiple short-wavelength spin excitations which have no counterparts in the semiclassical spin-wave theory. We demonstrate a highly nontrivial field evolution of quasiparticles spectra on the way from one collinear state (UUD) to another one (FP) via the non-collinear V-phase (in which the longitudinal and the transverse channels are mixed). In particular, some parts of the spin-0 branch in the UUD state become parts of the spin-1 (magnon) branch in the FP phase whereas some parts of one magnon branch turn into parts of spin-2 branch. Such evolution would be very difficult to find by any conventional analytical approach. Our results are in good agreement with neutron experimental data obtained recently in $\rm Ba_3CoSb_2O_9$, $\rm KYbSe_2$, and $\rm CsYbSe_2$.
