AI 中文总结
研究无长程磁序或轨道序时交替磁行为，用旋转不变格林函数方法分析相关模型，得出超过临界值出现复合态、激发光谱分裂等结果，确立了无长程序的“交替磁顺磁体”或“交替磁液体”概念。
AI 中文摘要
最初为具有轨道自由度的过渡金属化合物开发的Kugel-Khomskii自旋-赝自旋模型，最近在交替磁性的背景下被重新诠释。在这项工作中，我们从理论上研究了在没有长程磁序或轨道序的情况下交替磁行为的出现。使用旋转不变格林函数方法对正方形晶格和线性链上的SU(2)×SU(2)对称模型进行分析，我们分析了自旋-自旋和自旋-赝自旋相关函数、激发光谱、热容量和磁化率。我们表明，超过临界子系统间交换Kc(T)，会出现具有非零自旋-赝自旋相关性的复合态，尽管每个位点的平均自旋和赝自旋为零。激发光谱分裂为声学和光学分支，沿qx = qy有节线——交替磁对称性的直接特征。在相边界处观察到热容量峰值和磁化率跃变。在一维中，相边界是非单调的，并表现出再入转变。这些结果确立了“交替磁顺磁体”或“交替磁液体”的概念，其无长程序，与低维和强波动系统相关。
英文摘要
The Kugel-Khomskii spin-pseudospin model, originally developed for transition-metal compounds with orbital degrees of freedom, has recently been reinterpreted in the context of altermagnetism. In this work, we theoretically investigate the emergence of altermagnetic behavior in the absence of long-range magnetic or orbital order. Using the rotation-invariant Green's function method for the SU(2) x SU(2) symmetric model on a square lattice and on a linear chain, we analyze spin-spin and spin-pseudospin correlation functions, excitation spectra, heat capacity, and susceptibilities. We show that beyond a critical intersubsystem exchange Kc(T), a composite state arises with nonzero spin-pseudospin correlations, even though the average spin and pseudospin at each site are zero. The excitation spectrum splits into acoustic and optical branches, with nodal lines along qx = qy - a direct signature of altermagnetic symmetry. A peak in heat capacity and a jump in susceptibility are observed at the phase boundary. In 1D, the phase boundary is nonmonotonic and demonstrates reentrant transition. These results establish the concept of an "altermagnetic paramagnet" or "altermagnetic liquid" without long-range order, relevant for low-dimensional and strongly fluctuating systems.
