发表机构
The Pennsylvania State University（宾夕法尼亚州立大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文采用自洽相场理论，揭示SrTiO$_3$中极性纳米区形成源于极性与AFD涨落的杂化，解释了其类重入铁电行为，还预测了弱应变SrTiO$_3$的类重入序列。
AI 中文摘要
近期对量子顺电SrTiO$_3$的实空间成像研究[Nature 656, 54 (2026)]显示，局部极性结构不会随冷却持续增长，而是在60-65 K左右的中间温度达到强度峰值，随后向量子顺电基态再次减弱。这种局部极性结构的类重入减弱现象，挑战了“有序倾向通常随热涨落被抑制而增强”的传统范式。本文采用自洽相场理论表明，这种反常行为自然源于本征极性与反铁畸变相（AFD）涨落的相互作用。研究证实，类挠曲电耦合会使极性模式与AFD模式发生强杂化；当未杂化的极性模式与AFD模式在52 K附近交叉时，二者的杂化达到最大，驱动较低的杂化分支在有限波矢壳上出现极小值，这种有限q软化触发了Brazovskii型不稳定性，大幅增强极化关联并产生纳米级极性结构。偏离交叉温度后，两种模式失谐程度增加，杂化及相关的有限q软化随之减弱。这些结果揭示了SrTiO$_3$中极性纳米区形成的起源，自然解释了其意外局限于中间温度窗口的现象，提供了超越实验提出的量子涨落机制的新解释；此外，本文还预测弱应变SrTiO$_3$中存在非常规类重入序列：从零温度加热时，会依次经历铁电、顺电、极性纳米区，最终回到顺电态。
英文摘要
Recent real-space imaging in quantum paraelectric SrTiO$_3$ [Nature 656, 54 (2026)] reveals that local polar textures do not continuously grow upon cooling, but reach a maximum intensity at intermediate temperatures around 60-65 K and weaken again toward the quantum paraelectric ground state. Such a reentrant-like weakening of local polar textures challenges the conventional paradigm in which ordering tendencies generally continue to strengthen as temperature decreases. Here we employ a self-consistent phase-field theory showing that this anomalous behavior naturally arises from the coupling between intrinsic polar and antiferrodistortiv (AFD) fluctuations. We demonstrate that the flexoelectric-like coupling strongly hybridizes the polar and AFD modes. As the uncoupled polar and AFD modes cross near 52 K, their hybridization is maximized, driving the lower hybridized branch to develop a minimum on a finite-wave-vector shell. This finite-$q$ softening triggers a Brazovskii-type instability, strongly enhancing polarization correlations and producing nanoscale polar textures. Away from the crossing temperature, the two modes become increasingly detuned, weakening their hybridization and the associated finite-$q$ softening. These results reaveal the origin of the formation of polar nanoregions in SrTiO$_3$, naturally explaining the unexpected confinement to an intermediate-temperature window and providing a mechanism beyond the quantum-fluctuation-based interpretation suggested by experiment. Furthermore, we predict an unconventional reentrant-like sequence in weakly strained SrTiO$_3$, evolving from ferroelectric to paraelectric, polar-nanoregion, and eventually paraelectric regimes upon heating from zero temperature.
Comments6 pages, 4 figures
