Quantum Hall Effect in Stoichiometry‐Engineered β‐Ag2Te

Accessing surface quantum transport in topological insulators is hampered by residual bulk conduction arising from lattice defects. Here, we demonstrate a novel synthesis pathway for realizing high‐mobility ‐ thin films in which surface transport is dominant. An in situ room‐temperature Te treatment modifies the film stoichiometry, enabling continuous tuning of the sheet carrier density over more than an order of magnitude through the charge‐neutrality point without an external gate electrode. In the lower‐carrier‐density films, a fully developed quantum Hall state is observed, and Landau‐level energies extracted across samples collapse onto the relation, providing evidence for the massless Dirac dispersion of the top and bottom surface states. These results establish stoichiometry engineering as a lithography‐ and gate‐free approach to accessing quantum Hall transport in epitaxial topological‐insulator thin films.