In ionic Raman scattering, infrared-active phonons mediate a scattering process that results in the creation or destruction of a Raman-active phonon. This mechanism relies on nonlinear interactions between phonons and has in recent years been associated with a variety of emergent lattice-driven phenomena in complex transition-metal oxides, but the underlying mechanism is often obscured by the presence of multiple coupled order parameters in play. Here, we use time-resolved spectroscopy to compare coherent phonons generated by ionic Raman scattering with those created by more conventional electronic Raman scattering on the nonmagnetic and non-strongly-correlated wide-band-gap insulator ${\mathrm{LaAlO}}_3$. We find that the oscillatory amplitude of the low-frequency Raman-active $E_g$ mode exhibits a sharp peak when we tune our pump frequency into resonance with the high-frequency infrared-active $E_u$ mode, consistent with first-principles calculations. Our results suggest that ionic Raman scattering can strongly dominate electronic Raman scattering in wide-band-gap insulating materials. We also see evidence of competing scattering channels at fluences above $28\mathrm{mJ}/{\mathrm{cm}}^2$ that alter the measured amplitude of the coherent phonon response.

中文翻译：

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LaAlO3中电子和离子拉曼散射产生相干声子的比较

在离子拉曼散射中，红外活性声子会介导散射过程，从而导致拉曼活性声子的产生或破坏。该机制依赖于声子之间的非线性相互作用，并且近年来已与复杂过渡金属氧化物中各种新兴的晶格驱动现象相关联，但其潜在机制通常由于正在运行中存在多个耦合阶数参数而被掩盖。在这里，我们使用时间分辨光谱法将离子拉曼散射产生的相干声子与非磁性和非强相关宽带绝缘子上更常规的电子拉曼散射产生的相干声子进行比较。${\mathrm{拉铝}}_3$。我们发现低频拉曼有源的振荡幅度${Ë}_G$ 当我们将泵浦频率调整为与高频红外有源谐振时，该模式会显示一个尖峰 ${Ë}_{ü}$模式，与第一性原理计算一致。我们的结果表明，离子型拉曼散射可以在宽带隙绝缘材料中强烈地控制电子拉曼散射。我们还看到了在上述注量下竞争散射通道的证据$28\mathrm{兆焦耳}/{\mathrm{厘米}}^2$ 会改变所测量的相干声子响应的幅度。