Scientists discover a quantum effect that could eliminate batteries
Article excerpt
Researchers have discovered how microscopic imperfections and atomic vibrations can be used to control a powerful quantum effect in an advanced material. The effect can turn alternating electrical signals from the environment directly into the kind of current electronic devices need, without traditional components. As temperature changes, the signal can even flip direction, giving scientists a new way to tune device performance.
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 $β$-Ag$_2$Te thin films where surface transport is dominant. An \textit{in-situ} vacancy engineering step as part of the molecular beam epitaxy growth process acts to modify the stoichiometry and suppress donor-type defects, 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 $ν=1$ quantum Hall state is observed, and Landau-level energies extracted across samples collapse onto the $E_N=v_\mathrm{F}\sqrt{2e\hbar NB}$ relation, providing evidence for the massless Dirac dispersion of the top and bottom surface states. These results establish stoichiometry-driven vacancy engineering as a versatile lithography- and gate-free approach to accessing quantum Hall transport in epitaxial topological-insulator thin films.