Nanoscale Phonon Spectroscopy Reveals Emergent Interface Vibrational Structure of Superlattices

Abstract

As the length-scales of materials decrease, heterogeneities associated with interfaces approach the importance of the surrounding materials. Emergent electronic and magnetic interface properties in superlattices have been studied extensively by both experiments and theory. ${}^{1-6}$ However, the presence of interfacial vibrations that impact phonon-mediated responses, like thermal conductivity ${}^{7,8}$, has only been inferred in experiments indirectly. While it is accepted that intrinsic phonons change near boundaries ${}^{9,10}$, the physical mechanisms and length-scales through which interfacial effects influence materials remain unclear. Herein, we demonstrate the localized vibrational response associated with the interfaces in SrTiO${}_3$-CaTiO${}_3$ superlattices by combining advanced scanning transmission electron microscopy imaging and spectroscopy and density-functional-theory calculations. Symmetries atypical of either constituent material are observed within a few atomic planes near the interface. The local symmetries create local phonon modes that determine the global response of the superlattice once the spacing of the interfaces approaches the phonon spatial extent. The results provide direct visualization and quantification, illustrating the progression of the local symmetries and interface vibrations as they come to determine the vibrational response of an entire superlattice; stated differently, the progression from a material with interfaces, to a material dominated by interfaces, to a material of interfaces as the period decreases. Direct observation of such local atomic and vibrational phenomena demonstrates that their spatial extent needs to be quantified to understand macroscopic behavior. Tailoring interfaces, and knowing their local vibrational response, provides a means of pursuing designer solids having emergent infrared and thermal responses.

38 pages, 3 figures, 10 supplemental figures

References in corpus (2)

• Substrate coherency-driven octahedral rotations in perovskite oxide films
• First-principles study of the mobility of SrTiO${}_3$

Cited by in corpus (10)

• Atomic-scale observation of localized phonons at FeSe/SrTiO3 interface
• Correlated Quantum Phenomena of Spin-Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3-Based Artificial Superlattices
• Using Electron Energy-Loss Spectroscopy to Measure Nanoscale Electronic and Vibrational Dynamics in a TEM
• A roadmap for edge computing enabled automated multidimensional transmission electron microscopy
• Gigantic-oxidative atomic-layer-by-layer epitaxy for artificially designed complex oxides
• Emergent half-metal with mixed structural order in (111)-oriented (LaMnO${}_3$)${}_{2n}$|(SrMnO${}_3$)${}_n$ superlattices
• Single-dislocation phonons: atomic-scale measurement and their thermal properties
• Atomic-scale mapping of interfacial phonon modes in epitaxial YBa2Cu3O7-δ / (La,Sr)(Al,Ta)O3 thin films: The role of surface phonons
• Spectroscopic Observation and Modeling of Photonic Modes in CeO2 Nanocubes
• Platform and Framework for Time-Resolved Nanoscale Thermal Transport Measurements in STEM