Soon after two-dimensional electron gases (2DEG) had become commonly available for experiments, research groups attempted to create structures that could be called 2D artificial crystals. The idea is to subject the electrons confined to an interface between two semiconductors (i.e. along z -direction) to an additional modulation potential V (x, y). Contrary to the classical superlattices (1D/3D, that is 1D modulation of electrons in 3D bulk) described above, this is typically achieved by treating the heterostructure surface: depositing a suitably patterned metallic gate or etching. If the amplitude of V (x, y) is large (take V ( x , y ) = − − V 0 ( cos ⁡ ⁡ 2 π π x / a + cos ⁡ ⁡ 2 π π y / a ) , V 0 > 0 as an example) compared to the Fermi level, | V 0 | ≫ ≫ E f , the electrons in the superlattice should behave similarly to electrons in an atomic crystal with square lattice (in the example, these "atoms" would be located at positions (na, ma) where n, m are integers).