/cc) to CNP and beyond*

We report a new powerful method for tuning chemical potential in topological materials, capable of changing carrier densities by more than 10²⁰/cc. It involves the incorporation of H⁺ into the device structure. The process is reversible by low-temperature annealing (< 100^oC), and a finetuning of the chemical potential is easily achieved. We demonstrate this method to be effective in a variety of 3D bulk topological insulators (TIs) (e.g. Bi₂Te₃ and Sb₂Te₃), as well as in intrinsic magnetic TIs, such as Mn(Bi, Sb)₂Te₄. For example, Bi₂Te₃ which is initially p-type with hole carrier densities of >10¹⁹/cc is converted to n-type with n >10¹⁹/cc. This electron doping method should apply to other materials as well. Using a proper annealing protocol, the chemical potential is finetuned across the charge-neutral point (CNP), where the Hall resistance exhibits the ambipolar behavior and R_xx has a maximum at the type conversion. This method does not create additional defects that reduce carrier mobility, nor induce any significant top-bottom surface asymmetries typical of electrostatic gating. The mechanism responsible for the H⁺ doping will be discussed.