Quantum Spin Hall States and Topological Phase Transition in Germanene
Pantelis Bampoulis, Carolien Castenmiller, Dennis J. Klaassen, Jelle van Mil, Yichen Liu, Cheng‐Cheng Liu, Yugui Yao, Motohiko Ezawa, А. Н. Руденко, Harold J. W. Zandvliet
Abstract
We present the first experimental evidence of a topological phase transition in a monoelemental quantum spin Hall insulator. Particularly, we show that low-buckled epitaxial germanene is a quantum spin Hall insulator with a large bulk gap and robust metallic edges. Applying a critical perpendicular electric field closes the topological gap and makes germanene a Dirac semimetal. Increasing the electric field further results in the opening of a trivial gap and disappearance of the metallic edge states. This electric field-induced switching of the topological state and the sizable gap make germanene suitable for room-temperature topological field-effect transistors, which could revolutionize low-energy electronics.