Composition Dependence of the Electron Fermi Surfaces Tilt in Bi sub 1--x Sb sub x Alloys (0 < = x < = 0.22)

The composition dependence of the Fermi surfaces tilt out of the basal plane in Bi sub 1--x Sb sub x alloys (0 < = x < = 0.22) is determined by investigating the anisotropy of the propagation of magneto-plasma waves in the Voigt configuration B perpindicular to C sub 2 || k . In the semimetallic phase (0 < = x < = 0.07) no change is observed whereas in the semiconducting phase (0.07 < = x < = 0.22) a strong composition dependence is obtained, which is marked distinctly especially near the semimetal--semiconductor phase transitions (at x approx 0.07 and x approx 0.22) and in the composition region 0.15 < x < 0.18. The dispersion relation of the charge carriers, which is based on the deformation theory, connects the characteristics of the Fermi surfaces with the sublattice displacement, the rhombohedral shear and the spin-orbit coupling. A first analysis indicates that those composition dependences of these quantities which may cause the complex change of the charge carrier spectrum found are more complicated than assumed till now. 20 ref.--AA