Figure 2.

(a) Nodal line (in red) in the BZ and its projection on the (001), (010), and (100) planes (in grey). The parameters are set as C₁ = 1mF, C₂ = 2mF, C₃ = 1mF, C₄ = 0.833mF, C_GA = C_GB = 1mF, and L_A = L_B = 1mH. (b) Band structure along Γ − X − A − B − X − Γ, where A and B are two points with k_c = 0 on the nodal line as labeled in (a). (c) The band dispersions with the surface states (red colour lines) on the (001) surface. The drumhead-like surface states are nestled inside the projection of the nodal ring. (d) The Berry phase θ_k|| equals π for k_|| inside the nodal ring, while it is zero for k_|| outside the nodal ring.