Guzmán-Verri G G, Liang C H, Littlewood P B
Centro de Investigación en Ciencia e Ingeniería de Materiales, Universidad de Costa Rica, San José 11501, Costa Rica; Escuela de Física, Universidad de Costa Rica, San José 11501, Costa Rica; and Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, United Kingdom.
Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA; James Franck Institute, University of Chicago, Chicago, Illinois 60637, USA; and Argonne National Laboratory, Materials Science Division, Lemont, Illinois 60439, USA.
Phys Rev Lett. 2023 Jul 28;131(4):046801. doi: 10.1103/PhysRevLett.131.046801.
We consider a standard Ginzburg-Landau model of a ferroelectric whose electrical polarization is coupled to gradients of elastic strain. At the harmonic level, such flexoelectric interaction is known to hybridize acoustic and optic phonon modes and lead to phases with modulated lattice structures that precede the state with spontaneously broken inversion symmetry. Here, we use the self-consistent phonon approximation to calculate the effects of thermal and quantum polarization fluctuations on the bare hybridized modes to show that such long-range modulated order is unstable at all temperatures. We discuss the implications for the nearly ferroelectric SrTiO_{3} and KTaO_{3}, and we propose that these systems are melted versions of an underlying modulated state that is dominated by nonzero momentum thermal fluctuations except at the very lowest temperatures.
我们考虑一个铁电体的标准金兹堡-朗道模型，其电极化与弹性应变梯度耦合。在谐波水平上，已知这种挠曲电相互作用会使声学和光学声子模式发生杂化，并导致具有调制晶格结构的相，该相先于具有自发破缺反演对称性的状态出现。在此，我们使用自洽声子近似来计算热极化涨落和量子极化涨落对裸杂化模式的影响，以表明这种长程调制序在所有温度下都是不稳定的。我们讨论了对近铁电体SrTiO₃和KTaO₃的影响，并提出这些体系是一种潜在调制态的熔化版本，该调制态除了在非常低的温度下外，主要由非零动量热涨落主导。
