We report cyclotron resonance measurements in high-purity tellurium at submillimeter wavelength confirming that the isoenergetic surfaces involved at low magnetic fields are ellipsoids grouped by pairs symmetrical with respect to the Brillouin-zone corners. We explain the violent perturbation of the Landau levels at high magnetic field by assuming the ellipsoids to coalesce into dumb-bell surfaces, as for the Shubnikov-de Haas effect.

• Received 4 February 1969

DOI:https://doi.org/10.1103/PhysRevLett.22.890