Gedik等人最近报道的飞秒laser脉冲诱导铜酸盐HTSC材料晶体学膨胀的负U解释
A negative-U interpretation of the femto-second laser pulse induced crystallographic expansion of a cuprate HTSC material reported recently by Gedik et al
摘要：
Gedik等人最近使用泵浦/探测飞秒激光技术证明，在1.55 eV的脉冲激光光激发后，LaCuO 4 +d的c轴晶格参数暂时膨胀多达2.5%。访问一个平衡的亚稳态激发态观察到发展的时间尺度为30 ps。随后，后一种状态衰变，显示出略高于300 ps的更长半衰期。Gedik等人在标准p-到-d，O-到-Cu，电荷转移激发的框架内解释了这种激光诱导的状态间转移的温度独立性和亚稳态群体的产生对起始光脉冲每单位面积传递的能量的线性依赖性（超过关键阈值通量）。相比之下，这些相同的数据在这里重新解释泵本地对，在负U的情况下，铜酸盐HTSC的行为长期倡导的当前作者。在负U状态人口（10 CuIII 2-）的d8-至d10激光诱导的增强带来了显着的c轴膨胀凭借（i）局部静电荷不平衡，（ii）增加的反键性质的电子双负载d10（p6）配置创建在对接受CuIII配位单元，和（iii）的铜酸盐晶体结构的分层性质。新的意见是通过Rohlers罢工，标准的晶体学观察，条纹域的形成，和以前的泵/探测实验。
英文摘要：
Gedik et al have very recently demonstrated using a pump/probe femto-second laser technique that the c-axis lattice parameter of LaCuO4+d temporarily becomes expanded by as much as 2.5% following pulsed laser optical excitation at 1.55 eV. Access to an out-of-equilibrium metastable excited state is observed to develop on a time scale of 30 ps. Subsequently the latter state decays displaying a still longer half-life of just over 300 ps. Observation of the temperature independence of this laser induced interstate transfer and of the linear dependence of the production of the metastable population upon the energy delivered per unit area by the initiating light pulse (beyond a key threshold fluence) have been interpreted by Gedik et al within the framework of standard p-to-d, O-to-Cu, charge transfer excitations. By contrast these same data are reinterpreted here in terms of pumped local pairs, within a negative-U scenario of cuprate HTSC behaviour long advocated by the current author. The d8-to-d10 laser-induced augmentation in the negative-U state population (10CuIII2-) brings marked c-axis expansion by virtue of (i) the local electrostatic charge imbalance, (ii) the increased antibonding nature of the electron double-loading d10(p6) configuration created at pair-receptive CuIII coordination units, and (iii) the layered nature of the cuprate crystal structure. The new observations are related through to Rohlers striking, standard crystallographic observations, to the stripe domain formation, and to previous pump/probe experiments.
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