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

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. We also numerically verify our theory for these polymer systems.