Edge states at the interface of non-Hermitian systems

Yüce, C.

doi:10.1103/physreva.97.042118

Cited by 104 publications

(60 citation statements)

References 35 publications

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“…Our gain/loss-dressed photonic graphene always preserves P (as well as M x ) symmetry even when γ a = γ b and it is known that spatial symmetry is crucial for stabilizing higher-order corner modes [41,43]. In previous works, the topological properties of the PT -symmetric systems usually originate from the Hermitian parts of Hamiltoinians [57][58][59][60], but in our work non-Hermitian parts (patterned gain and loss) are crucial to induce the nontrival phase. Moreover, current PT -symmetric topological systems concern mainly 1D systems and the discussion of PT symmetry is limited to conventional topolog- ical phases [7,23,55,60,61], but our model presents a 2D higher-order counterpart.…”

Section: Discussionmentioning

confidence: 62%

Wannier-type photonic higher-order topological corner states induced solely by gain and loss

Liu

Hou

2020

Phys. Rev. A

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Photonic crystals have provided a controllable platform to examine excitingly new topological states in open systems. In this work, we reveal photonic topological corner states in a photonic graphene with mirror-symmetrically patterned gain and loss. Such a nontrivial Wannier-type higherorder topological phase is achieved through solely tuning on-site gain/loss strengthes, which leads to annihilation of the two valley Dirac cones at time-reversal-symmetric point, as the gain and loss change the effective tunneling between adjacent sites. We find that the symmetry-protected photonic corner modes exhibit purely imaginary energies and the role of Wannier center as topological invariant is illustrated. For experimental considerations, we also examine the topological interface states near a domain wall. Our work introduces an interesting platform for non-Hermiticity-induced photonic higher-order topological insulators, to which, with current experimental technologies, can be readily accessed.

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Section: Discussionmentioning

confidence: 62%

Wannier-type photonic higher-order topological corner states induced solely by gain and loss

Liu

Hou

2020

Phys. Rev. A

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“…First, the topological edge and defect states have finite imaginary eigenvalues [ Fig. 9 (b)], namely net gain or loss in their dynamics [95,96]. Second, the conventional Zak phase [97] becomes continuous then fails to be a good topological number of this non-Hermitian system [98,99].…”

Section: The Complex Ssh Modelmentioning

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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“…The nontrivial bulk topology in Hermitian systems can * wuyajie@xatu.edu.cn † Junpeng.Hou@utdallas.edu be detected by defects, such as edges, π-flux, dislocations and vortices [48][49][50][51][52][53]. When it comes to non-Hermitian systems, stable edge states could also exist at the interface between topological and trivial phases [54][55][56][57][58][59][60][61][62]. These topological states, originated from bulk topologies, are immune to local symmetry-preserved perturbations.…”

Section: Non-hermitian Hamiltonian Captures Essentials Of Open Systemmentioning

confidence: 99%

Symmetry-protected localized states at defects in non-Hermitian systems

Hou

2019

Phys. Rev. A

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Understanding how local potentials affect system eigenmodes is crucial for experimental studies of nontrivial bulk topology. Recent studies have discovered many exotic and highly non-trivial topological states in non-Hermitian systems. As such, it would be interesting to see how non-Hermitian systems respond to local perturbations. In this work, we consider chiral and particlehole -symmetric non-Hermitian systems on a bipartite lattice, including SSH model and photonic graphene, and find that a disordered local potential could induce bound states evolving from the bulk. When the local potential on a single site becomes infinite, which renders a lattice vacancy, chiral-symmetry-protected zero-energy mode and particle-hole symmetry-protected bound states with purely imaginary eigenvalues emerge near the vacancy. These modes are robust against any symmetry-preserved perturbations. Our work generalizes the symmetry-protected localized states to non-Hermitian systems.

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Edge states at the interface of non-Hermitian systems

Cited by 104 publications

References 35 publications

Wannier-type photonic higher-order topological corner states induced solely by gain and loss

Wannier-type photonic higher-order topological corner states induced solely by gain and loss

Active topological photonics

Symmetry-protected localized states at defects in non-Hermitian systems

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