Non-Hermitian band topology in active and dissipative mechanical metamaterials

Colin Scheibner, William T. M. Irvine, Vincenzo Vitelli

Published 2020-01-14Version 1

Networks of masses with transverse spring-like interactions provide a simple model of solids with energetic gain and loss. In this Letter, we study the non-Hermitian band topology of this model, which applies not only to active solids but also to gyroscopic metamaterials with dissipation. We examine a family of lattices in which topologically charged bands arise as activity (dissipation) is increased (decreased). The topological transition proceeds by a mechanism absent in Hermitian systems: Dirac cones spread out into exceptional rings rather than acquiring a gap. Above the transition, we observe chiral edge modes with a penetration depth that does not diverge even when the band gap closes.