Topological states at exceptional points

Yüce, C.

doi:10.1016/j.physleta.2019.05.031

Cited by 5 publications

(1 citation statement)

References 90 publications

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“…defective complex-gap closings, will be classified separately [154]. They can also be symmetry protected [155][156][157] and are featured by topological indices that can lead to topological states. The topological classification of EPs suggests that some robust photonic defect states in early reports would be EP-based [112,158,159].…”

Section: Complex Bandgap and Emergent Non-hermitian Topological Effectsmentioning

confidence: 99%

Active topological photonics

et al. 2020

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Topological photonics has emerged as a novel route to engineer the flow of light. Topologically-protected photonic edge modes, which are supported at the perimeters of topologically-nontrivial insulating bulk structures, have been of particular interest as they may enable low-loss optical waveguides immune to structural disorder. Very recently, there is a sharp rise of interest in introducing gain materials into such topological photonic structures, primarily aiming at revolutionizing semiconductor lasers with the aid of physical mechanisms existing in topological physics. Examples of remarkable realizations are topological lasers with unidirectional light output under time-reversal symmetry breaking and topologically-protected polariton and micro/nano-cavity lasers. Moreover, the introduction of gain and loss provides a fascinating playground to explore novel topological phases, which are in close relevance to non-Hermitian and paritytime symmetric quantum physics and are in general difficult to access using fermionic condensed matter systems. Here, we review the cutting-edge research on active topological photonics, in which optical gain plays a pivotal role. We discuss recent realizations of topological lasers of various kinds, together with the underlying physics explaining the emergence of topological edge modes. In such demonstrations, the optical modes of the topological lasers are determined by the dielectric structures and support lasing oscillation with the help of optical gain. We also address recent researches on topological photonic systems in which gain and loss themselves essentially influence on topological properties of the bulk systems. We believe that active topological photonics provides powerful means to advance micro/nanophotonics systems for diverse applications and topological physics itself as well.

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Section: Complex Bandgap and Emergent Non-hermitian Topological Effectsmentioning

confidence: 99%

Active topological photonics

et al. 2020

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Anomalous features of non-Hermitian topological states

Yüce

2020

Annals of Physics

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Topological states in non-Hermitian systems are known to exhibit some anomalous features. Here, we find two new anomalous features of non-Hermitian topological states. We consider a one dimensional nonreciprocal Hamiltonian and show that topological robustness can be practically lost for a linear combination of topological eigenstates in non-Hermitian systems due to the non-Hermitian skin effect. We consider a two dimensional non-Hermitian Chern insulator and show that chirality of topological states can be broken at some parameters of the Hamiltonan. This implies that the topological states are no longer immune to backscattering in 2D. arXiv:2002.11105v1 [cond-mat.mes-hall]

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Non-Hermitian anomalous skin effect

Yüce

2020

Physics Letters A

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A non-Hermitian topological insulator is fundamentally different from conventional topological insulators. The non-Hermitian skin effect arises in a nonreciprocal tight binding lattice with open edges. In this case, not only topological states but also bulk states are localized around the edges of the nonreciprocal system. We discuss that controllable switching from topological edge states into topological extended states in a chiral symmetric non-Hermitian system is possible. We show that the skin depth decreases with non-reciprocity for bulk states but increases with it for topological zero energy states.

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Topological states at exceptional points

Cited by 5 publications

References 90 publications

Active topological photonics

Active topological photonics

Anomalous features of non-Hermitian topological states

Non-Hermitian anomalous skin effect

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