Spectral diagrams of Hofstadter type for the Bloch electron in three dimensions

Flux-energy and angle-energy diagrams for an exact three-dimensional Hamiltonian of the Bloch electron in a uniform magnetic field are analyzed. The dependence of the structure of the diagrams on the direction of the field, the geometry of the Bravais lattice and the number of atoms in an elementary cell is considered. Numerical evidence is given that the angle-energy diagram may have a fractal structure even in the case of a cubic lattice. It is shown that neglecting coupling of Landau bands changes considerably the shape of the diagrams.