Lecture
Van Marum Mini Symposium
- Prof. Harold Zandvliet (UTwente), Prof. Richard van de Sanden (TUe)
- Date
- Wednesday 5 February 2025
- Time
- Location
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- BE.0.08
Harold Zandvliet: Germanene: a monoelemental 2D topological insulator
Germanene, i.e. the germanium analogue of graphene, shares many properties with graphene. Both materials host Dirac fermions, but there are also a few differences: (1) the spin-orbit coupling in germanene is much larger than in graphene and (2) the honeycomb lattice of germanene is not flat, but buckled. The large spin-orbit gap in germanene makes this material the ideal candidate to test the Kane-Mele model [1]. We show that germanene is a quantum spin Hall insulator with a gapped interior and topologically protected helical edge states [2]. The buckling of the lattice of the honeycomb allows to tailor the quantum state of matter of germanene. By applying a perpendicular electric field, the spin-orbit gap in germanene first closes and then reopens again. The reopening of the gap is accompanied by a topological phase transition of germanene from a two-dimensional topological insulator to a trivial band insulator. This electric field-induced tailoring of the quantum state of matter of germanene allows to controllably switch the topologically protected helical edge states on and off. The latter makes germanene the material of choice for the realization of a topological field-effect transistor.
References
- C. L. Kane and E. J. Mele, Quantum spin Hall effect in graphene, Phys. Rev. Lett. 95, 226801 (2005).
- P. Bampoulis, C. Castenmiller, D.J. Klaassen, J. van Mil, Y. Liu, C.-C. Liu, Y. Yao, M. Ezawa, A.N. Rudenko and H.J.W. Zandvliet, Quantum Spin Hall States and Topological Phase Transition in Germanene, Phys. Rev. Lett. 130, 196401 (2023).