  Well-known conductive molecular wires, like cumulene or polyyne, provide a
model for interconnecting molecular electronics circuit. In the recent
experiment, the appearance of carbon wire bridging two-dimensional electrodes -
graphene sheets - was observed [PRL 102, 205501 (2009)], thus demonstrating a
mechanical way of producing the cumulene. In this work, we study the structure
and conductance properties of the carbon wire suspended between carbon
nanotubes (CNTs) of different chiralities (zigzag and armchair), and
corresponding conductance variation upon stretching. We find the geometrical
structure of the carbon wire bridging CNTs similar to the experimentally
observed structures in the carbon wire obtained between graphene electrodes. We
show a capability to modulate the conductance by changing bridging sites
between the carbon wire and CNTs without breaking the wire. Observed current
modulation via cumulene wire stretching/elongation together with CNT junction
stability makes it a promising candidate for mechano-switching device for
molecular nanoelectronics.
