Question

Why does the energy gap of sublattice-symmetric systems never close?

Answer 1

The energy gap of sublattice-symmetric systems never closes because of the symmetry of the wave functions. When the symmetric state becomes the ground state, the energy gap remains open.

Step-by-step explanation:

The energy gap of sublattice-symmetric systems never closes because of the symmetry of the wave functions. In sublattice-symmetric systems, the ground state wave function is symmetric, while the first excited state wave function is antisymmetric. When the two wells of the system are brought closer, the symmetric state becomes the ground state due to its lower energy. Thus, the energy gap remains open.