Comparison of coherent phonon generation by electronic and ionic Raman scattering in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>LaAlO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>
Martin J. Neugebauer, Dominik M. Juraschek, Matteo Savoini, Pascal Engeler, Larissa Boie, Elsa Abreu, Nicola A. Spaldin, Steven L. Johnson
Abstract
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 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 mJ/cm 2 that alter the measured amplitude of the coherent phonon response.