Fig. 4: Theoretical model.

a Schematic representation of the TI-based Josephson junction in our theoretical model. We assume the TSS wavefunctions extend over the entire circumference of the TI as shown by the black circle in this figure. The pairing amplitude Δ is a piecewise constant function of x, as follows: Δ(x) = Δ₀ exp(iφ/2) for L/2 < x < L/2 + b, Δ₀exp(−iφ/2) for −L/2−b < x < −L/2, and zero otherwise. b Energy spectrum (energy E vs. phase φ) of the modes with k_y = 0 and energies within the superconducting gap Δ₀ (the lowest energy ones are highlighted with red) and parameters (L = 100 nm, b = 300 nm, C_x = 6 μm, Δ₀ = 0.3 meV, μ′ = 50 meV, and ħv_F = 1 eV Å) of sample A.