Surface Loving and Surface Avoiding modes

TL;DR

This paper analyzes the propagation of acoustic waves in GaAs/AlAs superlattices, identifying two types of surface-related modes—Surface Loving and Surface Avoiding—and discusses their observability and potential applications.

Contribution

It introduces the concept of Surface Loving modes, expanding the understanding of surface wave modes in superlattices and their experimental observability.

Findings

Surface avoiding modes have been experimentally observed.

Surface loving modes are theoretically shown to be observable.

Envelope phase and dephasing are key parameters for mode behavior.

Abstract

We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focussing on periodic modes in the vicinity of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared to its surface is a key parameter. We exhibit two kind of modes: Surface Avoiding and Surface Loving Modes whose envelope functions have their minima and respectively maxima in the vicinity of the surface. We finally consider the observability of such modes. While Surface avoiding modes have experimentally been observed (Phys. Rev. Lett. 97, 1224301 (2006)), we show that Surface Loving Modes are likely to be observable and we discuss the achievement of such experiments. The proposed approach could be easily transposed to other types of wave propagation in unidimensional semi-infinite periodic structures as photonic Bragg mirror.