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Anomalous Landau quantization in intrinsic magnetic topological insulators

The intrinsic magnetic topological insulators, Mn(Bi1-xSbx)2Te4, in their spin-aligned strong field configuration have been identified as a Weyl semimetal with single pair of Weyl nodes1-4. A direct consequence of the Weyl state is the layer-dependent Chern number (C) in thin film quantization. Previous reports in MnBi2Te4 thin films revealed the higher C states in the spin alignment by either increasing the film thickness5 or controlling chemical potential into electron doping6-8. A clear picture of the higher Chern states is still missing as the situation is complicated by the emerging of surface band Landau levels (LLs) in magnetic field. Here, we report a tunable layer-dependent of C= 1 state with the Sb substitutions by performing a detailed analysis of the quantization states in Mn(Bi1-xSbx)2Te4 dualgated devices, consistent with the calculations of the bulk Weyl point separations in the compounds. The observed Hall quantization plateaus for our thicker Mn(Bi1-xSbx)2Te4 films under strong magnetic fields can be interpreted from a theory of surface and bulk spin-polarized Landau levels spectrum in thin film magnetic topological insulators. Our results demonstrate that Mn(Bi1-xSbx)2Te4 thin films provide a highly tunable platform for probing the physics of the anomalous Landau quantization that is strongly sensitive to magnetic order.