Electron-lattice interactions strongly renormalize the charge-transfer energy in the spin-chain cuprate Li2CuO2.
Electron-lattice interactions strongly renormalize the charge-transfer energy in the spin-chain cuprate Li2CuO2.
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DOI：
10.1038/ncomms10563
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发表时间：
2016-02-17
影响因子：
16.6
通讯作者：
van den Brink J
中科院分区：
文献类型：
--
作者：
Johnston S;Monney C;Bisogni V;Zhou KJ;Kraus R;Behr G;Strocov VN;Málek J;Drechsler SL;Geck J;Schmitt T;van den Brink J
强相关绝缘体大致分为两类：Mott-Hubbard绝缘体，其中绝缘间隙由过渡金属阳离子上的库仑排斥U驱动；电荷转移绝缘体，其中间隙由阳离子和配体阴离子之间的电荷转移能Δ驱动。U和Δ的相对大小决定了一种物质属于哪一类，并随后决定了它的低能激发的性质。这些能量尺度通常是通过活性离子的局部化学来理解的。这里我们展示了低维电荷转移绝缘体Li_2CuO_2的情况更为复杂，其中Δ具有较大的非电子元件。结合共振非弹性X射线散射和详细的模型，我们确定了基本晶格、电荷、自旋和轨道激发是如何在这种材料中纠缠的。这导致了Δ的大规模晶格驱动的重整化，这极大地重塑了Li2CuO2的基本电子性质。在过渡金属氧化物中，当与离子电荷激发有关的能量尺度超过电子巡游时，发现了绝缘带隙。在这里，作者展示了Li2CuO2中强烈的电子-声子相互作用及其对绝缘带隙的影响。
Strongly correlated insulators are broadly divided into two classes: Mott–Hubbard insulators, where the insulating gap is driven by the Coulomb repulsion U on the transition-metal cation, and charge-transfer insulators, where the gap is driven by the charge-transfer energy Δ between the cation and the ligand anions. The relative magnitudes of U and Δ determine which class a material belongs to, and subsequently the nature of its low-energy excitations. These energy scales are typically understood through the local chemistry of the active ions. Here we show that the situation is more complex in the low-dimensional charge-transfer insulator Li2CuO2, where Δ has a large non-electronic component. Combining resonant inelastic X-ray scattering with detailed modelling, we determine how the elementary lattice, charge, spin and orbital excitations are entangled in this material. This results in a large lattice-driven renormalization of Δ, which significantly reshapes the fundamental electronic properties of Li2CuO2. In transition metal oxides, an insulating band gap is found when the energy scales related to ionic charge excitations dominate over electronic itinerancy. Here, the authors demonstrate strong electron-phonon interactions in Li2CuO2 and their effect on the insulating band gap.