Abstract

Realizing and controlling lower‐dimensional topological phases is key to realizing novel quantum devices. Here, we demonstrate a unified platform based on ultrathin, zigzag‐terminated germanene nanoribbons that (1) host a one‐dimensional topological insulator phase with strong spin–orbit coupling and (2) allow reversible, electric‑field control of their zero‑dimensional end modes in a vertical tunnel‑junction geometry at 77 K. Using a segregation-epitaxy method we were able to fabricate arrays of germanene nanoribbons with various widths. When their width exceeds a critical ∼2 nm threshold, topological edge states run around the nanoribbon as expected for the 2D parent phase. However, below this limit, the edge modes hybridize, and robust end states emerge, indicating the emergence of a 1D topological insulator. By tuning the perpendicular electric field in the scanning tunneling microscopy junction, we achieved on/off switching of these end states. This atomic‑scale, field‑effect control of symmetry‑protected 0D modes establishes a proof‐of‐principle of a topological field‑effect switch, opening pathways toward ultra‑small memory, robust qubits, and neuromorphic components.