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This research presents a novel mechanism for generating robust helical edge states in stacked quantum spin Hall systems using non-Hermitian feedback amplification rather than traditional symmetry protection. By demonstrating stability across irregular boundaries and intermediate coupling regimes, the study offers a new pathway for engineering topological devices that do not rely on strict time-reversal symmetry. These findings advance the theoretical understanding of non-Hermitian physics and could influence future designs in quantum transport architectures.
Beyond symmetry protection: Robust feedback-enforced edge states in non-Hermitian stacked quantum spin Hall systems
arXiv:2507.17295v3 Announce Type: replace-cross Abstract: Conventional wisdom holds that, in the simplest time-reversal-symmetric setting, strongly coupling two QSH layers yields a trivial $\mathbb Z_2$ phase and no protected topological edge states. We demonstrate that, in a regime with intermediate inter-layer coupling (neither in the strong or weak coupling regimes) and competitive non-Hermitian directed amplification, bulk modes are rendered with negligible gain while arbitrary bulk excitations inevitably accumulate into robust helical edge transport modes -- without relying on any symmetry protection. Our feedback-enforced mechanism persists over broad parameter ranges and remains robust even on fractal or irregular boundaries. These findings challenge the traditional view of stacked QSH insulators as inevitably trivial, and open up new avenues for designing helical topological devices that exploit feedback-enforced non-Hermitian engineering, instead of symmetry-enforced robustness.
Abstract:Conventional wisdom holds that, in the simplest time-reversal-symmetric setting, strongly coupling two QSH layers yields a trivial $\mathbb Z_2$ phase and no protected topological edge states. We demonstrate that, in a regime with intermediate inter-layer coupling (neither in the strong or weak coupling regimes) and competitive non-Hermitian directed amplification, bulk modes are rendered with negligible gain while arbitrary bulk excitations inevitably accumulate into robust helical edge transport modes -- without relying on any symmetry protection. Our feedback-enforced mechanism persists over broad parameter ranges and remains robust even on fractal or irregular boundaries. These findings challenge the traditional view of stacked QSH insulators as inevitably trivial, and open up new avenues for designing helical topological devices that exploit feedback-enforced non-Hermitian engineering, instead of symmetry-enforced robustness.
Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Other Condensed Matter (cond-mat.other); Mathematical Physics (math-ph); Computational Physics (physics.comp-ph); Quantum Physics (quant-ph)
arXiv:2507.17295 [cond-mat.mes-hall]
(or arXiv:2507.17295v3 [cond-mat.mes-hall] for this version)
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