Achieving charge neutrality in the intrinsic topological antiferromagnet by hydrogenation.

Magnetism combined with the nontrivial band topology by breaking time reversal symmetry will gap out otherwise gapless topological surface states, allowing novel topological quantum phases, such as quantum anomalous Hall or axion insulator, to emerge. The newly discovered intrinsic topological magnets in the MnBi₂Te₄ class are potentially able to host new topological phases at higher temperatures, however bulk conduction in these materials is high (in the 10²⁰ /cc range). Alloying Bi with Sb can provide charge compensation but this process is known to alter the bandstructure of MnBi_2-xSb_xTe₄. Here we show that charge compensation can be achieved continuously by hydrogenation without any changes in the bandstructure. We demonstrate ambipolar conduction and reversible tuning of the Fermi level E_F across the charge neutral point (CNP) in the 80 nm thick antiferromagnetic MnBi_2-xSb_xTe₄ using ionic hydrogen [1]. Near the CNP we explore surface/edge transport by finetuning E_F using electrostatic gating — transport under various hydrogenation conditions will be discussed. The technique shows promise for harnessing emergent topological quantum phenomena, such as axion physics, as well as higher-order topological orders.