氢键方酸晶体中偶极-偶极相互作用诱导相
Dipole-dipole interaction induced phases in Hydrogen-bonded squaric acid crystal
摘要：
本文研究了准二维氢键体系方酸晶体（$\text{H}_2\text{C}_4\text{O}_4$）质子有序的有限温度相图。我们考虑零阶四自旋相互作用模型。在随机级数展开量子蒙特卡罗方法中使用即兴循环算法，当我们增加温度和磁场时，我们发现两个不同的阶段。其中一个相是具有长程铁电有序的$Π_f$相，另一个相是具有强局域关联的中间态，即量子类液体态$Π_{ql}$。转变为$Π_{f}$时，比热出现一个非常小的反常峰，且临界温度与偶极-偶极相互作用的强度密切相关。小峰的存在归因于在偶极-偶极相互作用的存在下宏观简并的缺乏以及在小温度下这种简并在一定程度上的重新进入。虽然零阶四自旋相互作用和适当的二自旋相互作用模型的简并基态流形是相同的，但我们发现，对于前一种情况，诱导铁电相所需的偶极-偶极相互作用强度要大得多.这项工作还提出了一个复杂的联系，量子涨落和热涨落的竞争相互作用与熵效应的存在。
英文摘要：
We study analytically the finite-temperature phase diagram of proton ordering of a quasi-two dimensional hydrogen-bonded system, namely the squaric acid crystal($\text{H}_2\text{C}_4\text{O}_4$). We take into account the four-spin interaction model at the zeroth order. Using an improvised loop algorithm within the Stochastic series expansion quantum monte carlo method, we find two distinct phases as we increase the temperature and magnetic-field. One of the phase is the $Π_f$, the phase with long range ferroelectric order and the other being an intermediate state with strong local correlations, i.e, a quantum liquid-like state $Π_{ql}$. The transition to $Π_{f}$ shows a very small anomalous peak in the specific heat with strong dependence of critical temperature on the strength of dipole-dipole interaction. The presence of the small peak is attributed to the absence of macroscopic degeneracy in the presence of dipole-dipole interaction and re-entrance of such degeneracy to some extent at small temperature. Though the degenerate ground state manifold is identical for a four-spin interaction or appropriate two-spin interaction model at zeroth order, we find that for the former case, the required strength of dipole-dipole interaction is quite larger to induce a ferroelectric phase. The work also presents an intricate connection of quantum fluctuation and thermal fluctuation in the presence of competing interaction with entropic effects.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
