Parity-Time Synthetic Phononic Media

Classical systems containing cleverly devised combinations of loss and gain elements constitute extremely rich building units that can mimic non-Hermitian properties, which conventionally are attainable in quantum mechanics only. Parity-time (PT) symmetric media, also referred to as synthetic media, have been devised in many optical systems with the ground breaking potential to create nonreciprocal structures and one-way cloaks of invisibility. Here we demonstrate a feasible approach for the case of sound where the most important ingredients within synthetic materials, loss and gain, are achieved through electrically biased piezoelectric semiconductors. We study first how wave attenuation and amplification can be tuned, and when combined, can give rise to a phononic PT synthetic media with unidirectional suppressed reflectance, a feature directly applicable to evading sonar detection.J. C. gratefully acknowledges financial support from the Danish Council for Independent Research and a Sapere Aude Grant (No. 12-134776). V. R. V. gratefully acknowledges financial support from the Spanish Ministerio de Economía y Competitividad through Grant No. MAT2015-66888-C3-1-R