标题： 掺杂对SrTiO$_{3}$中极性有序的影响的第一性原理模拟 显示英文标题

标题： Effects of doping on polar order in SrTiO$_{3}$ from first-principles modeling

摘要： SrTiO$_{3}$是一种潜在的铁电体，也是一种异常稀释的超导体，其超导特性随载流子浓度呈类似圆顶的依赖关系。通过化学替代或应变稳定极性相，可以显著提高超导临界温度，这表明极性不稳定性与非常规库珀对之间可能存在某种联系。为了研究掺杂对 SrTiO$_{3}$中极性序的影响，我们开发了一个简化的自由能模型，该模型仅包含捕捉掺杂、双轴压缩应变系统相关物理现象所需的自由度。我们使用蒙特卡洛方法模拟不同掺杂水平下的极性和反铁畸变热相变，并讨论相变温度的掺杂依赖性以及极性纳米畴的形成。此外，利用朗之万模拟计算了温度相关的声子谱函数，以研究掺杂系统的晶格动力学。我们还研究了掺杂对极性相中电子结构的影响，包括态密度和能带分裂。最后，我们计算了 Rashba 参数的极化依赖性和 Mgdall 比的掺杂依赖性，并将我们的结果置于所提出的配对机制的更广泛背景下。 显示英文摘要

摘要： SrTiO$_{3}$ is an incipient ferroelectric and an exceptionally dilute superconductor with a dome-like dependence on carrier concentration. Stabilization of a polar phase through chemical substitution or strain significantly enhances the superconducting critical temperature, suggesting a possible connection between the polar instability and unconventional Cooper pairing. To investigate the effects of doping on the polar order in SrTiO$_{3}$, we develop a simplified free energy model which includes only the degrees of freedom necessary to capture the relevant physics of a doped, biaxially compressively strained system. We simulate the polar and antiferrodistortive thermal phase transitions using Monte Carlo methods for different doping levels and comment on the doping dependence of the transition temperatures and the formation of polar nanodomains. In addition, the temperature-dependent phonon spectral function is calculated using Langevin simulations to investigate the lattice dynamics of the doped system. We also examine the effects of doping on the electronic structure within the polar phase, including the density of states and band splitting. Finally, we compute the polarization dependence of the Rashba parameter and the doping dependence of the Midgal ratio, and place our results in the broader context of proposed pairing mechanisms.