从维度约化到混合铁-反铁呼吸烧绿石中的四聚化
From dimensional reduction to tetramerization in mixed ferro-antiferro breathing pyrochlores
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- Indian Institute of Technology Madras（印度理工学院马德拉斯分校）
- CNRS, University of Bordeaux（法国国家科学研究中心，波尔多大学）
- Ludwig-Maximilians-Universität München（慕尼黑路德维希-马克西米利安大学）
- HUN-REN Wigner Research Centre for Physics（匈牙利研究与教育网络温格物理研究中心）
- Helmholtz-Zentrum Berlin für Materialien und Energie（柏林亥姆霍兹材料能源中心）
- Freie Universität Berlin（柏林自由大学）
- University of Windsor（温莎大学）
- Institute for Solid State Physics and Optics（凝聚态物理与光学研究所）
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中文总结 AI 辅助
该研究通过多种数值方法，揭示了混合铁-反铁呼吸烧绿石中从维度约化到四聚化的转变，并预测了相关材料的磁有序。
中文摘要 AI 辅助
我们研究了呼吸烧绿石晶格上自旋-1/2最近邻海森堡模型在混合铁-反铁磁区域的行为，其中一种四面体子晶格为反铁磁性，另一种为铁磁性。经典基态流形由复合四面体矩构成的最近邻面心立方（fcc）反铁磁体的基态流形给出。经典蒙特卡洛模拟和自洽高斯近似表明，热致有序-通过无序机制消除了其亚广延简并性，并通过强一级相变选择了波矢为X=(1,0,0)的共线Type-I态。针对S=1/2和S=1的赝费米子泛函重整化群计算揭示了在退耦的反铁磁四面体极限附近存在一个非磁窗口，超出该窗口后X序重新出现。密度矩阵重整化群计算表明该窗口并非无特征：反铁磁四面体发展出近乎理想的四聚体关联，其中四个键携带⟨S_i·S_j⟩≈-1/2，而两个相对的键≈+1/4，同时结构因子在X处保持宽峰。四面体单态流形中的三阶有效哈密顿量解释了这一点：反转四面体间耦合的符号将Tsunetsugu的二聚体选择转化为均匀的四聚体选择，这一点通过精确对角化得到证实。动态高温展开追踪了局部四面体激发如何让位于低能X中心的谱权重。最后，我们将自旋-3/2呼吸铬硫尖晶石的八种结构的密度泛函参数置于经典相图中。该映射重现了CuInCr₄S₈的k=(1,0,0)有序，解释了LiGaCr₄S₈中无序的存在，并预测LiInCr₄S₈具有Type-I有序。
英文摘要
We study the spin-1/2 nearest-neighbor Heisenberg model on the breathing pyrochlore lattice in the mixed ferro-antiferromagnetic regime, where one tetrahedral sublattice is antiferromagnetic and the other ferromagnetic. The classical ground-state manifold is then that of the nearest-neighbor face-centered-cubic (fcc) antiferromagnet built from composite tetrahedral moments. Classical Monte Carlo simulations and the self-consistent Gaussian approximation show that thermal order-by-disorder lifts its subextensive degeneracy and selects the collinear Type-I state with wave vector $X=(1,0,0)$ through a strongly first-order transition. Pseudofermion functional renormalization group calculations for $S=1/2$ and $S=1$ reveal a nonmagnetic window adjacent to the decoupled antiferromagnetic-tetrahedron limit, beyond which $X$ order reappears. Density matrix renormalization group calculations show that this window is not featureless: the antiferromagnetic tetrahedra develop nearly ideal tetramer correlations, with four bonds carrying $\langle\mathbf{S}_i\cdot\mathbf{S}_j\rangle\simeq-1/2$ and the two opposite bonds $\simeq+1/4$, while the structure factor retains broad maxima at $X$. A third-order effective Hamiltonian in the tetrahedral-singlet manifold explains this: reversing the sign of the inter-tetrahedron coupling converts Tsunetsugu's dimer selection into a uniform tetramer selection, as confirmed by exact diagonalization. A dynamic high-temperature expansion traces how local tetrahedral excitations give way to low-energy $X$-centered spectral weight. Finally, we place density-functional parameters for eight structures of spin-3/2 breathing chromium thiospinels in the classical phase diagram. The mapping reproduces the $\mathbf{k}=(1,0,0)$ order of CuInCr$_4$S$_8$, accounts for the absence of order in LiGaCr$_4$S$_8$, and predicts Type-I order for LiInCr$_4$S$_8$.
