非线性双势阱中极化子迁移率的反常温度依赖：无偏X传播子方法
Anomalous temperature dependence of polaron mobility in a nonlinear double-well potential: unbiased X-propagator approach
AI总结：
该研究开发无偏X传播子方法，针对耦合双势阱晶格势的极化子，揭示其迁移率的反常温度依赖，为稀极性金属反常输运提供微观机制。
AI中文摘要：
我们开发了一种无偏X传播子方法，用于计算任意非线性电子-声子相互作用下的有限温度光导率σ(ω)和直流电迁移率μ。将该方法应用于耦合双势阱晶格势的极化子，这是强非简谐极性材料的最小模型。在中等耦合下，迁移率呈现三个温度区域，分别对应于单势阱内的受限、与势垒的热竞争以及与势垒无关的高温动力学。该序列产生了迁移率的凹形温度依赖，这在传统线性耦合极化子模型中不存在。在强耦合下，迁移率变为非单调，其温度演化反映在光谱权重的特征再分布中。对于与SrTiO₃相关的参数，我们的结果定性再现了反常凹形迁移率以及莫特-约费-雷格尔极限的违反起始，从而支持与软非简谐晶格模式的非线性耦合是稀极性金属中反常输运的微观机制。
英文摘要：
We develop an unbiased X-propagator method for calculating finite-temperature optical conductivity $σ(ω)$ and dc mobility $μ$ for arbitrary nonlinear electron-phonon interaction. We apply it to a polaron coupled to a double-well lattice potential, a minimal model for strongly anharmonic polar materials. At moderate coupling, the mobility exhibits three temperature regimes associated with confinement within one well, thermal competition with the barrier, and barrier-insensitive high-temperature dynamics. This sequence produces a concave temperature dependence of the mobility that is absent in conventional linear-coupling polaron models. At strong coupling, the mobility becomes nonmonotonic, and its temperature evolution is reflected in a characteristic redistribution of optical spectral weight. For parameters relevant to SrTiO$_3$, our results qualitatively reproduce both the anomalous concave mobility and the onset of violation of the Mott-Ioffe-Regel limit, thereby supporting nonlinear coupling to a soft anharmonic lattice mode as a microscopic mechanism for anomalous transport in dilute polar metals.
