论文标题
在yba $ _2 $ _2 $ _3 $ o $ $ _ {7-δ} $的选择性耦合yba $ _2 $ _2 $ _cu $ _3 $ _3
Selective coupling of coherent optical phonons in YBa$_2$Cu$_3$O$_{7-δ}$ with electronic transitions
论文作者
论文摘要
我们调查了最佳掺杂YBA $ _2 $ cu $ _3 $ o $ o $ _ {7-δ} $由Ultrashort驱动的（$ \ sim $ 12 fs）附近（NIR）和紫外线（NUV）脉冲附近的相干晶格动力学。瞬态反射率实验，在室温下和在中等（$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$ <$^$^2 $）的激发能力，显示$ a_g $ a_g $ -smmetry phonon模式与cuo $ _2 $中的o（2,3）弯曲相关的o（2,3）弯曲，并在频率上与频率（4）在频率之间进行5次和15 thz的频率，以及以前的10和15 thz，以及3.其他范围（以及以前的15 thz，defter），以及（另外）。和4.5 thz。相对相干的声子振幅与自发性拉曼散射光谱频谱上相同波长激发的相对声子强度形成鲜明对比。这种对比表示拉曼和非拉曼机制对相干声子的产生的模式依赖性贡献。我们表明，特别激烈的连贯的Cu（2）声子及其初始阶段主要通过位移机制支持其生成，可能涉及Cuo $ _2 $ planes中的电荷传递。在10 THz处相干外O（2,3）弯曲模式的小幅度也表明非兰面生成机制的参与。可以在拉曼机制的框架内原理解释其他连贯的声子的产生。当泵灯具有垂直于CuO $ _2 $平面的极化成分时，与面内激发相比，在15 THz处的相干O（4）模式得到了强烈增强，与面内激发相比，与顶端和链氧和链氧和O（O（4）和O（1）之间的跳跃相关的较大的极性分量。
We investigate coherent lattice dynamics in optimally doped YBa$_2$Cu$_3$O$_{7-δ}$ driven by ultrashort ($\sim$ 12 fs) near infrared (NIR) and near ultraviolet (NUV) pulses. Transient reflectivity experiments, performed at room temperature and under moderate ($<$0.1 mJ/cm$^2$) excitation fluence, reveal $A_g$-symmetry phonon modes related to the O(2,3) bending in the CuO$_2$ planes and to the apical O(4) stretching at frequencies between 10 and 15 THz, in addition to the previously reported Ba and Cu(2) vibrations at 3.5 and 4.5 THz. The relative coherent phonon amplitudes are in stark contrast to the relative phonon intensities in the spontaneous Raman scattering spectrum excited at the same wavelength. This contrast indicates mode-dependent contributions of the Raman and non-Raman mechanisms to the coherent phonon generation. We show that the particularly intense coherent Cu(2) phonon, together with its initial phase, supports its generation predominately via a displacive mechanism, possibly involving the charge transfer within the CuO$_2$ planes. The small amplitude of the coherent out-of-phase O(2,3) bending mode at 10 THz also suggests the involvement of non-Raman generation mechanism. The generation of the other coherent phonons can in principle be explained within the framework of Raman mechanism. When the pump light has the polarization component perpendicular to the CuO$_2$ plane, the coherent O(4) mode at 15 THz is strongly enhanced compared to the in-plane excitation, corresponding to the large polarizability component associated with the hopping between the apical and the chain oxygens, O(4) and O(1).
