Trigonal Warping of the Energy Surfaces in Tellurium

The period of the Shubinkov—de Haas oscillations, when the magnetic field is applied in the plane perpendicular to the $c$ axis of single-crystal heavily doped Te ($p=4.8\mathrm{}\times {10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$), is observed to depend on the azimuthal angle. This angular dependence gives clear experimental evidence of trigonal warping of the constant-energy surfaces about the $k_z$ axis in the Brillouin zone.