Bismuth, with its rhombohedral crystalline structure and two Raman active phonon modes corresponding to the internal displacement ($A_{1g}$) and shear ($E_{g}$) ionic motions, offers an ideal target for the investigation of the phonon-phonon and electron-phonon couplings under photoexcitation. We perform transient reflectivity measurements of bismuth single crystal at 11 K over wide range of absorbed laser fluence up to $F_\text{abs}=9$ mJ/cm$^2$, at which a sign of an irreversible surface damage is observed. At the minimum fluence examined (0.1 mJ/cm$^2$) the coherent $A_{1g}$ and $E_g$ oscillations are a cosine and a sine functions of time, as are consistent with their generations in the displacive and impulsive limits, respectively. With increasing fluence the initial phases of the both modes deviate from their low-fluence values, indicating a finite time required for the transition from the ground-state potential energy surface (PES) to the excited-state one. Surprisingly, the $E_g$ amplitude increases with increasing fluence up to 3 mJ/cm$^2$ and then turns to an apparent decrease, in contrast to the monotonic increase of the $A_{1g}$ amplitude up to 6 mJ/cm$^2$. The contrasted behaviors can be understood by considering a two-dimensional PES, where the strongly driven $A_{1g}$ oscillation leads to a temporal fluctuation of the PES along the $E_g$ coordinate and thereby to a loss in the $E_g$ oscillation coherence at high fluences.
Suppression of atomic displacive excitation in photo-induced A$_{\mathrm{1g}}$ phonon mode of bismuth unveiled by low-temperature time-resolved x-ray diffraction
Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: Direct measurements with atomic-column spatial resolution
Sparse Cyclic Excitations Explain the Low Ionic Conductivity of Stoichiometric Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$
我们已经进行了长时间尺度的分子动力学模拟的立方相和四方相的固体锂离子电解质Li $_{7}$ La $_{3}$ Zr $_{2}$ O $_{12}$（LLZO），使用第一性原理参数化的原子间势。集体锂运输进行了分析，确定动力学激发，持续离子位移的距离可比的锂网站之间的分离，和字符串样的离子簇进行合作运动。我们发现，在c-LLZO的动态激发是频繁的，与参与锂数遵循指数分布，反映了脆弱的玻璃的动态。相比之下，t-LLZO中的激发在时间和空间上都是稀疏的，优选地由围绕闭环的高度协调的锂运动组成。这种质的差异被解释为在t-LLZO中的锂排序的结果，并且提供了t-LLZO与c-LLZO相比的低得多的离子电导率的机理基础。
