Stable topological insulators achieved using high energy electron beams

Topological insulators are potentially transformative quantum solids with metallic surface states which have Dirac band structure and are immune to disorder. Ubiquitous charged bulk defects, however, pull the Fermi energy into the bulk bands, denying access to surface charge transport. Here we demonstrate that irradiation with swift (∼2.5 MeV energy) electron beams allows to compensate these defects, bring the Fermi level back into the bulk gap and reach the charge neutrality point (CNP). Controlling the beam fluence, we tune bulk conductivity from p - (hole-like) to n -type (electron-like), crossing the Dirac point and back, while preserving the Dirac energy dispersion. The CNP conductance has a two-dimensional character on the order of ten conductance quanta and reveals, both in Bi 2 Te 3 and Bi 2 Se 3 , the presence of only two quantum channels corresponding to two topological surfaces. The intrinsic quantum transport of the topological states is accessible disregarding the bulk size. Defects in solids may introduce additional charges that influence the overall charge transport behaviour. Here, Zhao et al . use swift electron beams to compensate charge defects, which effectively tune Bi 2 Te 3 and Bi 2 Se 3 from p -type to n -type while preserving their topological properties.