Electric-field control of zero-dimensional topological states in ultranarrow germanene nanoribbons

Abstract: Symmetry-protected zero-dimensional (0D) modes, such as corner and end states with fractionalized charge, promise robust qubits and efficient electronics. Yet, reversible, electric-field manipulation and control of these modes has remained elusive. Here, we show theoretically and experimentally electric-field-driven on/off switching of 0D topological end modes in two- and three-hexagon wide germanene nanoribbons in a vertical tunnel junction set-up. We demonstrate the annihilation and restoration of end states in topological samples, but also the induction of 0D topological modes in initially trivial ribbons. The process is reversible, and the system operates at 77 Kelvin. This atomic-scale platform realizes a proof-of-principle for a 0D topological field-effect device, opening an unexpected path for ultra-small memory, quantum computing, and neuromorphic architectures.