  Intrinsic bilayer graphene is a gapless semimetal. Under the application of a
bias field it becomes a semiconductor with a direct band gap that is
proportional to the applied field. Under a layer-asymmetric strain (where the
upper layer undergoes compression and lower layer tension or visa-versa) we
find that the band gap of a biased bilayer graphene ribbon becomes indirect
and, for higher strains, becomes negative returning the material its original
semimetal state. As a result, the conductivity of the ribbon increases and can
be almost an order of magnitude larger that of the intrinsic unbiased material
- a change that can be induced with a strain of only ~2-3%. The conductivity is
proportional to the applied strain and the magnitude of the effect is tunable
with the bias field. Such layer-asymmetric strains can be achieved by bending,
with forces on the order of ~1nN resulting in a layer-asymmetric strain of ~1%.
This new electromechanical effect has a wide potential for application in the
areas of nano-force microscopy and pressure sensing on the atomic scale.
