Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5
Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5
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DOI：
10.1038/nature13875
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发表时间：
2014-12-04
期刊：
影响因子：
64.8
通讯作者：
Cavalleri, A.
中科院分区：
文献类型：
--
作者：
Mankowsky, R.;Subedi, A.;Cavalleri, A.
太赫兹频率的光脉冲可以共振地驱动固体中选定的振动模式，并使其晶体结构变形(1-3)。在复合氧化物中，这种方法已经被用来熔化电子有序(4-6)，驱动绝缘体到金属的转变(7)和诱导超导(8)。值得注意的是，在IrBa2Cu3O6+x(参考文献9，10)中，在室温(300Kelvin)以下，可以瞬时地诱导出使人强烈联想到超导电性的共格层间输运。在这里，我们报道了这种奇特的非平衡态的晶体结构，由飞秒X射线衍射和从头算密度泛函理论计算确定。我们发现，正常态IrBa2Cu3O6-x在52Kelvin以上的转变温度下的非线性晶格激发引起了Cu-O-2双层内和双层间距离的同时增加和减少，并伴随着面内O-Cu-O键屈曲的各向异性变化。密度泛函理论计算表明，这些运动引起了电子结构的剧烈变化。其中，面内电子结构d(x2-y2)特征的增强可能有利于超导电性。
Terahertz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structures(1-3). In complex oxides, this method has been used to melt electronic order(4-6), drive insulator-to-metal transitions(7) and induce superconductivity(8). Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature (300 kelvin) in IrBa2Cu3O6+x (refs 9, 10). Here we report the crystal structure of this exotic non-equilibrium state, determined by femtosecond X-ray diffraction and ab initio density functional theory calculations. We find that nonlinear lattice excitation in normal-state IrBa2Cu3O6-x at above the transition temperature of 52 kelvin causes a simultaneous increase and decrease in the Cu-O-2 intra-bilayer and, respectively, inter-bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause drastic changes in the electronic structure. Among these, the enhancement in the d(x2-y2) character of the in-plane electronic structure is likely to favour superconductivity.