  We argue that twisted graphene nanoribbons subjected to a transverse electric
field can operate as a variety of nanoelectronic devices, such as tunable
tunnel diodes with current-voltage characteristics controlled by the transverse
field. Using the density-functional tight-binding method to address the effects
of mechanical strain induced by the twisting, we show that the electronic
transport properties remain almost unaffected by the strain in relevant cases
and propose a simplified tight-binding model which gives reliable results. The
transverse electric field creates a periodic electrostatic potential along the
nanoribbon, resulting in a formation of a superlattice-like energy band
structure and giving rise to different remarkable electronic properties. We
demonstrate that if the nanoribbon geometry and operating point are selected
appropriately, the system can function as a field-effect transistor or a device
with nonlinear current-voltage characteristic manifesting one or several
regions of negative differential resistance. The latter opens possibilities for
applications such as an active element of nanoscale amplifiers, generators, and
new class of devices with multiple logic states.
