Engineering novel quantum phases with germanene

The thesis examines germanene, a two-dimensional topological insulator with a sizeable band gap, and explores its topological properties and their possible uses and limits in low-energy electronics. It focuses on the quantum spin Hall effect, which allows dissipationless transport along material edges.

The work finds that germanene keeps these topological properties at room temperature, with robust metallic edge states that an external electric field can switch on and off. Edge termination influences Fermi velocity, with armchair edges higher than zigzag edges. In nanoribbons, the dimensional limits of the quantum spin Hall phase are studied: ribbons wider than about 2.6 nm show pronounced edge states, while narrower ones can become a one-dimensional topological crystalline phase with end states.