  In the field of nanomechanics, parametric excitations are of interest since
they can greatly enhance sensing capabilities and eliminate cross-talk.
However, parametric excitations often rely on externally tuned springs, which
limits their application to high quality factor resonators and usually does not
allow excitation of multiple higher modes into parametric resonance. Here we
demonstrate parametric amplification and resonance of suspended single-layer
graphene membranes by an efficient opto-thermal drive that modulates the
intrinsic spring constant. With a large amplitude of the optical drive, a
record number of 14 mechanical modes can be brought into parametric resonance
by modulating a single parameter: the pretension. In contrast to conventional
mechanical resonators, it is shown that graphene membranes demonstrate an
interesting combination of both strong nonlinear stiffness and nonlinear
damping.
