Evidence for a different dispersion of the topological edge state of germanene at armchair and zigzag edges

Utilizing a tunneling spectroscopy approach based on the energy-dependent inverse decay length, our research unveils distinct dispersion characteristics of germanene's topological edge states. We observe a pronounced variance in Fermi velocity, with armchair edges exhibiting a velocity higher than zigzag edges by about an order of magnitude. This difference highlights the influence of edge termination on the energy-momentum dispersion relation of one-dimensional topological edge states in two-dimensional topological insulators, aligning with the theoretical framework of a Kane-Mele topological insulator.