Transport signatures of gate-tunable topological phase transition in ultrathin β-Ag₂Te

The topological phase transition (TPT) between trivial and nontrivial quantum states has attracted significant research interests due to its fundamental importance in condensed matter physics and potential applications in next-generation low-power electronics. However, previous TPT has mainly been achieved by structural modification and chemical doping on topological materials, which presents substantial challenges for practical device applications. Here, we report the direct observation of device-level reversible TPT in β-Ag₂Te nanoflakes controlled by an out-of-plane gate voltage. The quantum oscillations in β-Ag₂Te exhibit a π Berry phase when applying a small top-gate voltage, while displaying a topologically trivial Berry phase under a high gate voltage. Theoretical calculations reveal that this electrically induced TPT originates from the Stark-effect-mediated band structure modification under external electric fields. Based on this gate-tunable TPT in β-Ag₂Te, we successfully fabricate the preliminary prototype device of TPT field-effect transistor, exhibiting a high current on-off ratio exceeding 10⁴. This work establishes an electric-field control paradigm for topological phase engineering, and builds a crucial bridge between fundamental topological physics and novel device concepts.