Quantum Hall Effect in Stoichiometry-Engineered β - Ag 2 Te

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 $\beta$ - ${\mathrm{Ag}}_2\mathrm{Te}$ 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 $\nu =1$ quantum Hall state is observed, and Landau-level energies extracted across samples collapse onto the $E_N=v_F\sqrt{2e\hslash NB}$ 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.