  It is a persisting pursuit to use metal as a channel material in a field
effect transistor. All metallic transistor can be fabricated from pristine
semimetallic Dirac materials (such as graphene, silicene, and germanene), but
the on/off current ratio is very low. In a vertical heterostructure composed by
two Dirac materials, the Dirac cones of the two materials survive the weak
interlayer van der Waals interaction based on density functional theory method,
and electron transport from the Dirac cone of one material to the one of the
other material is therefore forbidden without assistance of phonon because of
momentum mismatch. First-principles quantum transport simulations of the
all-metallic vertical Dirac material heterostructure devices confirm the
existence of a transport gap of over 0.4 eV, accompanied by a switching ratio
of over 104. Such a striking behavior is robust against the relative rotation
between the two Dirac materials and can be extended to twisted bilayer
graphene. Therefore, all-metallic junction can be a semiconductor and novel
avenue is opened up for Dirac material vertical structures in high-performance
devices without opening their band gaps.
