Topological surface currents accessed through reversible hydrogenation of the bulk*

Hydrogen, one of the most promising clean fuel alternatives if efficiently incorporated within a solid, can also drastically modify its electronic and structural state. Here we report a new hydrogenation approach resolving an outstanding challenge in chalcogenide classes of topological materials — the control of intrinsic bulk conduction — using an aqueous HCl solution rich in H⁺. The technique tunes carrier densities by over 10²⁰ cm^-3, moving the Fermi level across the surface states within the bulk gap to achieve ambipolar conduction from p (hole-like) to n-type (electron-like) and back. Electrons are donated by a weak binding of H⁺ to Te(Se) chalcogen, a bond controllably removed by a low-temperature anneal. We demonstrate hydrogen-tunability of the canonical TI, such as Bi₂Te₃ and Bi₂Se₃, and of the recently discovered intrinsic magnetic topological materials MnX₂Y₄ (X=Bi, Sb and Y=Te, Se) and their superlattices¹. The technique significantly expands the availability of robust materials platforms for harnessing emergent topological quantum phenomena and higher-order topological orders.

1: H. Deng, L. Krusin-Elbaum, et. al. High-temperature quantum anomalous Hall regime in a MnBi₂Te₄/Bi₂Te₃ superlattice. Nature Phys. (2020)