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Spectra and pseudo-spectra of tridiagonal k-Toeplitz matrices and the topological origin of the non-Hermitian skin effect

by H. Ammari and S. Barandun and Y. De Bruijn and P. Liu and C. Thalhammer

(Report number 2024-05)

Abstract
We establish new results on the spectra and pseudo-spectra of tridiagonal k-Toeplitz operators and matrices. In particular, we prove the connection between the winding number of the eigenvalues of the symbol function and the exponential decay of the associated eigenvectors (or pseudo-eigenvectors). Our results elucidate the topological origin of the non-Hermitian skin effect in general one-dimensional polymer systems of subwavelength resonators with imaginary gauge potentials, proving the observation and conjecture in [H. Ammari et al., arXiv:2307.13551]. We also numerically verify our theory for these systems.

Keywords: Tridiagonal k-Toeplitz operator, block-Toeplitz operator, Tridiagonal k-Laurent operator, pseudospectra, Coburn's lemma, non-Hermitian skin effect, gauge capacitance matrix, eigenmode condensation

@Techreport{ABDLT24_1087,
  author = {H. Ammari and S. Barandun and Y. De Bruijn and P. Liu and C. Thalhammer},
  title = {Spectra and pseudo-spectra of tridiagonal k-Toeplitz matrices and the topological origin of the non-Hermitian skin effect},
  institution = {Seminar for Applied Mathematics, ETH Z{\"u}rich},
  number = {2024-05},
  address = {Switzerland},
  url = {https://www.sam.math.ethz.ch/sam_reports/reports_final/reports2024/2024-05.pdf },
  year = {2024}
}

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