Data for: Non-linear optical phonon spectroscopy revealing polaronic signatures of the LaAlO3/SrTiO3 interface

We report the direct observation of lattice phonons confined at LaAlO3/SrTiO3 (LAO/STO) interfaces and STO surfaces using the sum-frequency phonon spectroscopy. This interface-specific nonlinear optical technique unveiled phonon modes localized within a few monolayers at the interface, with inherent sensitivity to the coupling between lattice and charge degrees of freedom. Spectral evolution across the insulator-to-metal transition at LAO/STO interface revealed an electronic reconstruction at the sub-critical LAO thickness, as well as strong polaronic signatures upon formation of the two-dimensional electron gas. We further discovered a characteristic lattice mode from interfacial oxygen vacancies, enabling us to probe such important structural defects in situ. Our study provides a new perspective on many-body interactions at the correlated oxide interfaces.

我们采用和频声子光谱（sum-frequency phonon spectroscopy），直接观测到了局限于铝酸镧（LaAlO3，简称LAO）/钛酸锶（SrTiO3，简称STO）界面以及STO表面的晶格声子。该界面特异性非线性光学技术，揭示了局限于界面处数单原子层内的声子模式，且对晶格与电荷自由度间的耦合具有本征敏感性。LAO/STO界面处绝缘体-金属转变过程中的光谱演化，揭示了亚临界LAO层厚度下的电子重构现象，以及二维电子气形成时出现的强极化子特征。我们还从界面氧空位中发现了一种特征晶格模式，使得我们能够原位探测这类重要的结构缺陷。本研究为关联氧化物界面处的多体相互作用研究提供了全新视角。