Engineering nanoscale hypersonic phonon transport

TL;DR

This paper demonstrates the engineering of silicon nanostructures to create a broad phononic band gap at room temperature, effectively suppressing mechanical vibrations and enabling localized GHz modes for advanced optomechanical applications.

Contribution

It introduces a method to achieve a broad phononic stop band in silicon nanostructures and demonstrates localized GHz mechanical modes at room temperature, advancing phonon control technologies.

Findings

Broad phononic band gap of 5.3 GHz centered at 8.4 GHz achieved.

Complete suppression of mechanical vibrations within the band gap.

Localized GHz mechanical modes observed in line-defect waveguides.

Abstract

Controlling the vibrations in solids is crucial to tailor their mechanical properties and their interaction with light. Thermal vibrations represent a source of noise and dephasing for many physical processes at the quantum level. One strategy to avoid these vibrations is to structure a solid such that it possesses a phononic stop band, i.e., a frequency range over which there are no available mechanical modes. Here, we demonstrate the complete absence of mechanical vibrations at room temperature over a broad spectral window, with a 5.3 GHz wide band gap centered at 8.4 GHz in a patterned silicon nanostructure membrane measured using Brillouin light scattering spectroscopy. By constructing a line-defect waveguide, we directly measure GHz localized modes at room temperature. Our experimental results of thermally excited guided mechanical modes at GHz frequencies provides an eficient platform for photon-phonon integration with applications in optomechanics and signal processing transduction.