Fig. 1: Quasicrystalline quadrupole topological insulators in electrical circuits.

a Schematic of the circuit with 69 unit cells. One unit cell consists of four sites labeled as 1, 2, 3, and 4 at the left-up corner. The colored sites are wired to grounded inductors and/or capacitors listed on the right. For example, the black hollow point 3 is connected to the ground by the capacitor–inductor pairs C₁ and L₁, and the yellow point 1 is connected to the ground by L_4g. The sites in the same unit cell are wired by intracell inductors L₁ (red dashed lines) and capacitors C₁ (red solid lines), and the intercell elements between the unit cells are inductors L₂ (gray dashed lines) and capacitors C₂ (gray solid lines). b Photo of the fabricated circuit. The yellow and black elements are capacitors and inductors, respectively, and the wirings are indicated on overlay of the printed circuit board.