  Subjecting a nanohelix to a transverse electric field gives rise to
superlattice behavior with tunable electronic properties. We theoretically
investigate such a system and find Bloch oscillations and negative differential
conductance when a longitudinal electric field (along the nanohelix axis) is
also applied. Furthermore, we study dipole transitions across the
transverse-electric-field-induced energy gap, which can be tuned to the
eulogized terahertz frequency range by experimentally attainable external
fields. We also reveal a photogalvanic effect by shining circularly polarized
light onto our helical quantum wire.
