  Topological properties in condensed matter physics are often claimed to be a
fruitful resource for technical applications, but so far they only play a minor
role in applications. Here we propose to put topological edge states to use in
tailored graphene for Fermi velocity engineering. By tuning external control
parameters such as gate voltages, the dispersions of the edge states regime are
modified in a controllable way. This enables the realizations of devices such
as tunable delay lines and interferometers with switchable delays.
