Figure 1.

(a) A selection of BLS spectra for different values of the parallel wavevector transfer q for the highly-doped (n_ = 7.5 · 10¹⁹ cm⁻³) thinner (50 nm) film of Bi₂Te₃(111) on a GaAs substrate (sample A) with no external magnetic field. (b) A few spectra of sample A measured with an external magnetic field (700 Oe) applied normal to the surface (black dots) are compared with the corresponding spectra at H = 0 (gray dots). Similarly in panel (c), where a comparison is made between some spectra for the thicker low-doped sample B at H = 0 (black dots) with the corresponding spectra of sample A (gray dots). In all panels blue and red arrows indicate features attributed to RW and LR modes, respectively.