Anomalous topological edge states in non-Hermitian piezophononic media

Abstract

The bulk-boundary or bulk-edge correspondence is a principle relating surface confined states to the topological classification of the bulk. By combining non-Hermitian ingredients in terms of gain or loss with media that violate reciprocity, an unconventional non-Bloch bulk-boundary correspondence leads to unusual localization of bulk states at boundaries$-$a phenomenon coined non-Hermitian skin effect. Here we \textcolor{black}{numerically} employ the acoustoelectric effect in electrically biased and layered piezophononic media as a solid framework for non-Hermitian and nonreciprocal topological mechanics in the MHz regime. Thanks to a non-Hermitian skin effect for mechanical vibrations, we find that the bulk bands of finite systems are highly sensitive to the type of crystal termination, which indicates a failure of using traditional Bloch bands to predict the wave characteristics. More surprisingly, when reversing the electrical bias, we unveil how topological edge and bulk vibrations can be harnessed either at the same or opposite interface. Yet, while bulk states are found to display this unconventional skin effect, we further discuss how in-gap edge states in the same instant, counterintuitively are able to delocalize along the entire layered medium. We foresee that our predictions will stimulate new avenues in echo-less ultrasonics based on exotic wave physics.

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• Enhancement of Second-Order Non-Hermitian Skin Effect by Magnetic Fields
• Non-Hermitian Maryland Model
• System size dependent topological zero modes in coupled topolectrical chains
• Always-Real-Eigenvalued Non-Hermitian Topological Systems
• Non-Hermitian Weyl semimetal and its Floquet engineering
• Phase transitions and bunching of correlated particles in a non-Hermitian quasicrystal
• Insensitive edge solitons in a non-Hermitian topological lattice
• Extended topological mode in a one-dimensional non-Hermitian acoustic crystal
• Tunable two-dimensional laser arrays with zero-phase locking
• Non-Hermitian extended midgap states and bound states in the continuum
• Topological Corner States in Graphene by Bulk and Edge Engineering
• Selective and tunable excitation of topological non-Hermitian skin modes
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• Versatile Control of Nonlinear Topological States in Non-Hermitian Systems
• Extended imaginary gauge transformation in a general nonreciprocal lattice
• Symmetry-driven Phononic Metamaterials
• Inverse Design of Winding Tuple for Non-Hermitian Topological Edge Modes
• Unified Multipole Bott Indices for Non-Hermitian Skin Effect in Different Orders
• Size-Dependent Skin Effect Transitions in Weakly Coupled Non-Reciprocal Chains
• Anti-parity-time topologically undefined state
• Self-healing of non-Hermitian topological skin modes