Baldini Edoardo, Sentef Michael A, Acharya Swagata, Brumme Thomas, Sheveleva Evgeniia, Lyzwa Fryderyk, Pomjakushina Ekaterina, Bernhard Christian, van Schilfgaarde Mark, Carbone Fabrizio, Rubio Angel, Weber Cédric
Institute of Physics, Laboratory for Ultrafast Microscopy and Electron Scattering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland;
Institute of Chemical Sciences and Engineering, Laboratory of Ultrafast Spectroscopy, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Proc Natl Acad Sci U S A. 2020 Mar 24;117(12):6409-6416. doi: 10.1073/pnas.1919451117. Epub 2020 Mar 11.
The role of the crystal lattice for the electronic properties of cuprates and other high-temperature superconductors remains controversial despite decades of theoretical and experimental efforts. While the paradigm of strong electronic correlations suggests a purely electronic mechanism behind the insulator-to-metal transition, recently the mutual enhancement of the electron-electron and the electron-phonon interaction and its relevance to the formation of the ordered phases have also been emphasized. Here, we combine polarization-resolved ultrafast optical spectroscopy and state-of-the-art dynamical mean-field theory to show the importance of the crystal lattice in the breakdown of the correlated insulating state in an archetypal undoped cuprate. We identify signatures of electron-phonon coupling to specific fully symmetric optical modes during the buildup of a three-dimensional (3D) metallic state that follows charge photodoping. Calculations for coherently displaced crystal structures along the relevant phonon coordinates indicate that the insulating state is remarkably unstable toward metallization despite the seemingly large charge-transfer energy scale. This hitherto unobserved insulator-to-metal transition mediated by fully symmetric lattice modes can find extensive application in a plethora of correlated solids.
尽管经过数十年的理论和实验研究，但晶格对铜酸盐及其他高温超导体电子性质的作用仍存在争议。虽然强电子关联范式表明绝缘体到金属转变背后存在纯粹的电子机制，但最近电子 - 电子相互作用和电子 - 声子相互作用的相互增强及其与有序相形成的相关性也受到了强调。在此，我们结合偏振分辨超快光学光谱和最先进的动态平均场理论，展示了晶格在典型未掺杂铜酸盐中相关绝缘态崩溃过程中的重要性。我们识别出在电荷光掺杂后三维（3D）金属态形成过程中，电子 - 声子耦合到特定完全对称光学模式的特征。沿相关声子坐标对相干位移晶体结构的计算表明，尽管电荷转移能量尺度看似很大，但绝缘态对金属化非常不稳定。这种迄今未观察到的由完全对称晶格模式介导的绝缘体到金属的转变可在大量相关固体中得到广泛应用。
