Mankowsky R, Fechner M, Först M, von Hoegen A, Porras J, Loew T, Dakovski G L, Seaberg M, Möller S, Coslovich G, Keimer B, Dhesi S S, Cavalleri A
Max Planck Institute for the Structure and Dynamics of Matter , Hamburg, Germany.
Max Planck Institute for Solid State Research , Stuttgart, Germany.
Struct Dyn. 2017 Feb 28;4(4):044007. doi: 10.1063/1.4977672. eCollection 2017 Jul.
Resonant optical excitation of apical oxygen vibrational modes in the normal state of underdoped YBaCuO induces a transient state with optical properties similar to those of the equilibrium superconducting state. Amongst these, a divergent imaginary conductivity and a plasma edge are transiently observed in the photo-stimulated state. Femtosecond hard x-ray diffraction experiments have been used in the past to identify the transient crystal structure in this non-equilibrium state. Here, we start from these crystallographic features and theoretically predict the corresponding electronic rearrangements that accompany these structural deformations. Using density functional theory, we predict enhanced hole-doping of the CuO planes. The empty chain Cu orbital is calculated to strongly reduce in energy, which would increase c-axis transport and potentially enhance the interlayer Josephson coupling as observed in the THz-frequency response. From these results, we calculate changes in the soft x-ray absorption spectra at the Cu -edge. Femtosecond x-ray pulses from a free electron laser are used to probe changes in absorption at two photon energies along this spectrum and provide data consistent with these predictions.
在欠掺杂YBaCuO的正常态中，对顶端氧振动模式进行共振光激发会诱导出一种瞬态，其光学性质与平衡超导态相似。其中，在光激发态中会瞬时观察到虚电导率发散和等离子体边缘。过去曾使用飞秒硬X射线衍射实验来确定这种非平衡态下的瞬态晶体结构。在此，我们从这些晶体学特征出发，从理论上预测伴随这些结构变形的相应电子重排。利用密度泛函理论，我们预测CuO平面的空穴掺杂增强。计算得出空链Cu轨道能量大幅降低，这将增加c轴输运，并可能增强层间约瑟夫森耦合，正如在太赫兹频率响应中所观察到的那样。根据这些结果，我们计算了Cu边软X射线吸收光谱的变化。利用自由电子激光产生的飞秒X射线脉冲来探测该光谱上两个光子能量处的吸收变化，并提供与这些预测一致的数据。
