偶极晶格玻色子相分离态的密度不稳定性与热稳定化
Density instabilities and thermal stabilization of phase separated states in dipolar lattice bosons
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中文总结 AI 辅助
本研究通过路径积分量子蒙特卡罗模拟，探究二维正方晶格硬核偶极玻色子的密度不稳定性，发现有限温度可稳定相分离态，其结构与实验观测的自束缚绝缘体相似。
中文摘要 AI 辅助
近期在光晶格中实现近简并偶极气体的进展，使研究具有长程各向异性相互作用的量子系统成为可能。本研究针对二维正方晶格上的硬核偶极玻色子，采用扩展Bose-Hubbard模型进行描述，在固定方位角φ=45°的条件下，通过路径积分量子蒙特卡罗模拟，探究一阶相变引发的密度不稳定性。首先绘制半填充时基态相图，作为偶极相互作用强度和极角θ的函数：弱相互作用下，系统在所有θ下均保持超流态；超过临界相互作用强度后，超流态失稳，根据θ的不同，依次变为棋盘相、条纹相或不可压缩相。当θ≳62°时，半填充态失稳，仅空态（n=0）和全填充态（n=1）稳定。与近期实验报道的半填充自束缚绝缘体不同，均匀基态不存在该相，而是呈现n=0与n=1间的直接一阶相变。有限温度下，热涨落将密度不稳定性的 onset 移至更大θ，并在基态下半填充不稳定的区域稳定中间填充态，形成由空区和全填充区组成的相分离态，其结构与实验观测到的“自束缚绝缘体”相似；在简谐势中，类似结构也由一阶相变关联的相共存产生。
英文摘要
Recent advances in realizing nearly degenerate dipolar gases in optical lattices have enabled the study of quantum systems with long-range anisotropic interactions. Here, we investigate hard-core dipolar bosons on a two-dimensional square lattice described by an extended Bose--Hubbard model. Using path-integral quantum Monte Carlo simulations at fixed azimuthal angle $φ=45^\circ$, we investigate density instabilities arising from first-order phase transitions. We start by mapping the ground-state phase diagram at half filling as a function of dipolar interaction strength and polar angle $θ$. For weak interactions, the system remains superfluid for all $θ$. Above a critical interaction strength, the superfluid phase becomes unstable and gives way to checkerboard, stripe, or incompressible phases depending on $θ$. For $θ\gtrsim 62^\circ$, we find that half filling becomes unstable and only the empty state, $n=0$, and the fully filled state, $n=1$, are stable. Unlike recent experimental reports of a self-bound insulator at half filling, the homogeneous ground state does not support such a phase, but instead exhibits a direct first-order transition between $n=0$ and $n=1$. At finite temperature, thermal fluctuations shift the onset of density instabilities to larger $θ$ and stabilize intermediate fillings in the regime where half filling is unstable in the ground state. This leads to phase-separated states consisting of empty and fully filled regions that resemble the experimentally observed "self-bound insulator." In a harmonic trap, similar structures also emerge from phase coexistence associated with the underlying first-order transition.
