On-chip unidirectional waveguiding for surface acoustic waves along a defect line in a triangular lattice

TL;DR

This paper presents a novel on-chip unidirectional surface acoustic wave (SAW) waveguide in a triangular lattice that is robust, broadband, and maintains zero Berry curvature, enabling efficient SAW routing with minimal reflection.

Contribution

It introduces a new topologically protected SAW waveguide based on intrinsic chirality and zero Berry curvature, distinct from previous spin or valley-polarized designs.

Findings

Wide bandwidth SAW confinement with 3 dB attenuation within half a unit cell

SAW routing around sharp bends with less than 4% reflection

Robustness of the waveguide to different defect line configurations

Abstract

The latest advances in topological physics have yielded a rich toolset to design highly robust wave transfer systems, for overcoming issues like beam steering and lateral diffraction in surface acoustic waves (SAWs). However, presently used designs for topologically protected SAWs have been largely limited to spin or valley-polarized phases, which rely on non-zero Berry curvature effects. Here we propose and experimentally demonstrate a highly robust SAW waveguide on lithium niobate (LiNbO3), based on a line defect within a true triangular phononic lattice, which instead employs an intrinsic chirality of phase vortices and maintains a zero Berry curvature. The guided SAW mode spans a wide bandwidth and shows confinement in the lateral direction with 3 dB attenuation within half of the unit-cell length. SAW routing around sharp bends has been demonstrated in such waveguide, with less than ~4% reflection per bend. The waveguide has also been found robust for defect lines with different configurations. The fully on-chip system permits unidirectional SAW modes that are tightly bound to the waveguide, which provides a compact footprint ideal for miniaturization of practical applications and offers insight into the possibility of manipulating highly focused SAW propagation.