  Graphene membranes suspended off electric contacts or other rigid supports
are prone to elastic strain, which is concentrated at the edges and corners of
the samples. Such a strain leads to an algebraically varying effective magnetic
field that can reach a few Tesla in sub-micron wide flakes. In the quantum Hall
regime the interplay of the effective and the physical magnetic fields causes
backscattering of the chiral edge channels, which can destroy the quantized
conductance plateaus.
