(a) A two-dimensional Lieb lattice. The unit cell contains three atoms: A (green dots), B (blue dots), and C (red dots). The solid lines represent NN hopping, and the dashed lines represent the NNN hopping with ISO coupling. (b) Scheme of the strip lattice with the straight edges. Both sides (the upper and lower boundaries in the y-axis direction) of the lattice constitute A and B atoms. Here and hereafter, a periodic boundary condition is imposed along the x-axis direction. (c) Scheme of the strip lattice with the bearded edges, in which both sides of the lattice are terminated with C atoms. (d) Scheme of the strip lattice under the asymmetry boundary condition, in which one side is terminated with the straight edge and the other with the bearded edge.