Fig. 1. The circuit design for the hybrid second-order skin-topological (ST) and skin-skin (SS) effects.

a Designed 2D electric circuit network with different values of intra-cell and inter-cell couplings. Each unit cell contains four sublattices (a, b, c, d). The blue lines with arrows represent INICs which can tune nonreciprocity in the circuit and the black lines denote inter-cell capacitive and inductive couplings. b, c Display the circuit unit for the realization of hybrid second-order ST effect and SS effect with C = 2.2 nF and L = 1.5 uH, respectively. Different colors of INIC indicate different values of non-Hermitian coupling. d Detail structures of different INICs. The components in the INIC(red): C₁ = 1nF, C₂ = 820 pF; INIC(green): C₁ = 1 nF, C₃ = 390 pF; INIC(blue): L₁ = 3.3 uH, L₂ = 3.9 uH, R_a = 20 Ω and C_a = 1 uF.