Robust localized zero-energy modes from locally embedded PT -symmetric defects

Abstract

We demonstrate the creation of robust localized zero-energy states that are induced into topologically trivial systems by the insertion of a PT-symmetric defect with local gain and loss. A pair of robust localized states induced by the defect turns into zero-energy modes when the gain-loss contrast exceeds a threshold, at which the defect states encounter an exceptional point. Our approach can be used to obtain robust lasing or perfectly absorbing modes in any part of the system.

Compatibility of transport effects in non-Hermitian nonreciprocal systems

“…Effectively non-Hermitian models have a long tradition in the description of states with a finite life time, with applications ranging from scattering resonances over quasiparticle dephasing to classical wave propagation with gain and loss [1][2][3]. Over the last few years, these endeavours have received substantial impetus by the realization that non-Hermitian physics can equip existing topological states with unique physical features, and also function as a source of topological effects in themselves [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. A particularly prominent manifestation is the non-Hermitian skin effect, in which the bulk states become localized at an edge of a finite system, resulting in a behaviour that is drastically different from its periodic counterpart [20][21][22][23][24][25][26][27][28][29][30][31][32][33].…”

Observation of Topological Edge States in Thermal Diffusion

“…[1][2][3][4] The topological band theory has revolutionized our understanding particularly parity-time symmetric wave systems, [25] enabling many intriguing phenomena such as parity-time symmetric topological edge states, [26] topological funneling, [27] bulk Fermi arcs, [28] and many others. [29][30][31][32] Another important natural existing physical dynamics, known as diffusion, has been widely studied in the context of heat transfer, [33] Brownian motion, [34] and so on. Unlike fields in wave systems (quantum mechanical or classical), diffusive fields are not governed by "frequency", and thus the phase no longer depends on time but solely on space.…”

Asymmetric Localization by Second Harmonic Generation

“…The method of generating a localized mode in periodic structures has paved its footprints in some photonics systems. One can achieve this localization by breaking the translation symmetry through embedding a defect in a periodic lattice [1][2][3][4][5][6]. Photonic crystal lasers [7][8][9], strain field traps [10], strong photon localization [11], and mode selection [12] are instances for applications of defect mode in periodic photonic systems.…”