Evidence for 2D conduction channels in hydrogenated Bi₂Te₃

Topological insulators are quantum solids with metallic surface states that have Dirac band structure and are immune to backscattering by the nonmagnetic disorder. However, ubiquitous charged bulk defects pull the Fermi energy into the bulk, denying access to surface charge transport. We demonstrate that by inserting/removing ionic hydrogen H⁺ in a bulk Bi₂Te₃ crystal, with hole densities in the 10²⁰ cm^-3 range, these defects can be compensated, moving the Fermi level across the charge neutral point (CNP) into the bulk gap. The magnetoresistance R_xx(H) evolves from a quadratic field dependence of a typical bulk metal into a weak antilocalization (WAL) regime with a characteristic low-field cusp near the CNP. From the fits to weak localization theory we obtain the cusp parameter α≅1.004 ± 0.005, corresponding to two 2D quantum conduction channels supported by top and bottom surfaces. The obtained temperature dependence of the dephasing length l_φ ∝1/√T is characteristic of the 2D quantum interference. The 2D character is further confirmed by the scaling of R_xx(H) with the out-of-plane field component H⊥= Hcos??. Our results show that the 2D quantum transport can be accessed by hydrogenation disregarding the 3D bulk size.