We report quantum oscillation studies on the $\mathrm{B}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_{3-x}{\mathrm{S}}_x$ topological insulator single crystals in pulsed magnetic fields up to 91 T. For the $x=0.4$ sample with the lowest bulk carrier density, the surface and bulk quantum oscillations can be disentangled by combined Shubnikov–de Haas and de Hass–van Alphen oscillations, as well as quantum oscillations in nanometer-thick peeled crystals. At high magnetic fields beyond the bulk quantum limit, our results suggest that the zeroth Landau level of topological surface states is shifted due to the Zeeman effect. The $g$ factor of the topological surface states is estimated to be between 1.8 and 4.5. These observations shed new light on the quantum transport phenomena of topological insulators in ultrahigh magnetic fields.

• Received 18 May 2015
• Revised 3 September 2015

DOI:https://doi.org/10.1103/PhysRevB.92.235402