Stretching induced Hall current and conductance anisotropy in graphene

We evaluate the effect of stretching on the optical conductance of a single layer graphene sheet. It is found that the low energy (Dirac regime) isotropy that leads to the `universal conductance' is lost. More significantly, due to the loss of C_3 symmetry, a non-zero Hall conductance emerges for stretching along chiral directions, reaching a maximum at a stretching angle of 45 degrees, and being as high a S_0 = e2/4h at van Hove singular point for bond angle changes of about 2 degrees.