  Dirac materials are characterized by energy-momentum relations that resemble
those of relativistic massless particles. Commonly denominated Dirac cones,
these dispersion relations are considered to be their essential feature. These
materials comprise quite diverse examples, such as graphene and topological
insulators. Band-engineering techniques should aim to a full control of the
parameter that characterizes the Dirac cones: the Fermi velocity. We propose a
general mechanism that enables the fine-tuning of the Fermi velocity in Dirac
materials in a readily accessible way for experiments. By embedding the sample
in a uniform electric field, the Fermi velocity is substantially modified. We
first prove this result analytically, for the surface states of a topological
insulator/semiconductor interface, and postulate its universality to other
Dirac materials. Then we check its correctness in carbon-based Dirac materials,
namely graphene nanoribbons and nanotubes, thus showing the validity of our
hypothesis in both continuum and tight-binding calculations and in different
Dirac systems.
