发表机构
Brown University; Ohio State University（布朗大学; 俄亥俄州立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过大规模经典蒙特卡洛模拟，发现5$d^1$双钙钛矿中热涨落熔化部分四极相，并证明FM[110]态为内禀量子相，而主要磁相在经典框架内稳健。
AI 中文摘要
自旋-轨道耦合的$d^1$双钙钛矿展现出自旋、轨道和四极自由度（DOF）之间丰富的相互作用，从而产生相互竞争的磁性和多极相。尽管量子平均场理论预测了许多奇异相，但它们对热涨落的稳定性以及在经典框架内的可重现性仍然是一个悬而未决的问题。在此，我们通过在FCC晶格的投影$j=3/2$流形上开展大规模经典蒙特卡洛模拟，超越了平均场的局限性，使得复杂的排序模式无需预设磁对称性即可自发涌现。我们的热力学映射揭示，热涨落在相图的一部分区域熔化了中温四极相，而在其他区域该相则完整存续。至关重要的是，通过系统地隔离经典与量子稳定性之间的边界，我们证明了四亚晶格反铁磁和铁磁（FM）相是稳健的经典相，而共面倾斜FM[110]态则完全失稳。这确定了FM[110]相是一种由量子涨落产生的内禀量子态。我们的结果表明，主要磁相在经典描述中是稳健的，系统的基本物理由弱纠缠、短程关联的DOF所捕获，并强调了热涨落在决定不同类型磁性和四极序稳定性中的作用。
英文摘要
Spin-orbit-coupled $d^1$ double perovskites exhibit a rich interplay of spin, orbital, and quadrupolar degrees of freedom (DOF), giving rise to competing magnetic and multipolar phases. Although quantum mean-field theories predict many exotic phases, their stability against thermal fluctuations and reproducibility within a classical framework remain an open question. Here, we surpass the mean-field limitations by deploying large-scale classical Monte Carlo simulations on the projected $j=3/2$ manifold of the FCC lattice, allowing complex ordering patterns to emerge spontaneously without preassigned magnetic symmetries. Our thermodynamic mapping reveals that thermal fluctuations melt the intermediate-temperature quadrupolar phase over part of the phase diagram, while it survives intact elsewhere. Crucially, by systematically isolating the boundary between classical and quantum stability, we demonstrate that while the four-sublattice antiferromagnetic and ferromagnetic (FM) phases are robustly classical, the coplanar canted FM[110] state completely destabilizes. This identifies the FM[110] phase as an intrinsically quantum state born out of quantum fluctuations. Our results demonstrate that the dominant magnetic phases are robust within a classical description, where the essential physics of the system is captured by weakly entangled, short-range correlated DOF and highlight the role of thermal fluctuations in determining the stability of different types of magnetic and quadrupolar order.
