Topological Modes in Non-Hermitian Phononic Crystals Optically Induced in a Quantum-Well Array

Abstract: Propagation of acoustic waves in a quantum-well array, in which spatially modulated sound amplification and attenuation are implemented by optical excitation at a frequency close to the exciton resonance, has been studied theoretically. Sound dispersion near Bragg resonances corresponding to the modulation wave vector is calculated. Occurrence of “imaginary” stop bands, in which imaginary parts of the Bloch mode frequencies are split, is described. It is demonstrated that acoustic topological modes arise at the structure edge.