Atomic-scale mapping of interfacial phonon modes in epitaxial YBa2Cu3O7-δ/(La,Sr)(Al,Ta)O3 thin films: The role of surface phonons

We investigate the behavior of phonons at the epitaxial interface between YBa2Cu3O7-δ thin film and (La,Sr)(Al,Ta)O3 substrate using vibrational electron energy loss spectroscopy. Interfacial phonon modes with different degrees of scattering localization were identified. We find evidence that surface contributions from the surrounding environment can impose additional scattering modulation onto local EELS measurements at the interface. A method to remove those contributions is then used to isolate the phonon information at the interface. This work unveils interfacial phonon modes in a high-Tc cuprate superconductor, that are not accessible with traditional phonon spectroscopy techniques, and provides a method for probing interfacial phonons in complex oxide heterostructures.