Formation of New Fermi Surfaces in 3D Crystals at Ultra High Magnetic Field with Different Orientations

In the tight-binding approximation the Harper like equation describing an electron in 3D crystal subject to a uniform magnetic field is obtained. It is supposed that the vector H can be oriented along several directions in the lattice. The Fermi surfaces relevant to a magnetic flux p/q=1/2 in a simple cubic lattice are built. The quantization rules in magnetic fields slightly distinguished from p/q=1/2 are investigated.