Observation of Surface-Avoiding Waves: A New Class of Extended States in Periodic Media

TL;DR

This paper reports the experimental discovery of surface-avoiding acoustic waves in superlattices, which are long-lived states that weakly interact with boundaries, with potential implications for surface science and resonant cavities.

Contribution

It provides the first experimental observation of surface-avoiding waves in a solid-state superlattice, demonstrating their existence and characteristics.

Findings

Long-lived acoustic mode at ~0.6 THz observed

Surface-avoiding waves occur outside forbidden gaps

Potential applications in surface science and resonant cavities

Abstract

Coherent time-domain optical experiments on GaAs-AlAs superlattices reveal the exis-tence of an unusually long-lived acoustic mode at ~ 0.6 THz, which couples weakly to the environment by evading the sample boundaries. Classical as well as quantum states that steer clear of surfaces are generally shown to occur in the spectrum of periodic struc-tures, for most boundary conditions. These surface-avoiding waves are associated with frequencies outside forbidden gaps and wavevectors in the vicinity of the center and edge of the Brillouin zone. Possible consequences for surface science and resonant cavity ap-plications are discussed.