Fig. 2

Topolectrical Su-Schrieffer–Heeger (SSH) circuit. a circuit diagram blueprint. Each unit cell consists of a pair of capacitors C₁ and C₂, with identical inductors L between every two capacitors. An alternate current (AC) source provides a driving voltage with amplitude V₀. For t = C₁/C₂ < 1, an SSH midgap mode is found. In the experimental implementation we set C₁ = 0.1 μF, C₂ = 0.22 μF and L = 10 μH. Green lines indicate wiring for measuring the t⁻¹-configuration on the same circuit. b Ideal impedance magnitude across the nodal ends a = 1 and b = N of an N = 10 SSH topolectrical circuit as a function of AC frequency ω for various values of t. The dashed curves highlight topologically trivial cases for t > 1, showing that the impedance increases enormously only for t < 1, the topologically nontrivial regime. The topolectrical boundary resonance (TBR) at \(\omega = \tilde \omega\) is most pronounced for the smallest t, and decreases exponentially as t is increased. Secondary resonances are observed at larger deviations from \(\tilde \omega\), and are associated with other eigenvalues of the grounded circuit Laplacian J. c Measurement of midgap voltage eigenmode ψ₀(n), which accurately fits the shape predicted by theory, i.e., ψ₀(n) = ((−t)ⁿV₀, 0) for the nth two-site unit cell from the left, see also a for node numbering. Associated errors are calculated from standard deviation and according linear regression analysis, but are smaller than the symbols. d Impedance measurement of the t = 0.22 and t⁻¹ = 4.5 configuration. Despite non-negligible serial resistance and element non-uniformities, the SSH midgap peak is observed in the impedance measurement but absent for the t⁻¹ = 4.5 configuration