  Recent advances in strain engineering at the nanoscale have shown the
feasibility to modulate the properties of graphene. Although the
electron-phonon (e-ph) coupling and Kohn anomalies in graphene define the
phonon branches contributing to the resonance Raman scattering, and is relevant
to the electronic and thermal transport as a scattering source, the evolution
of the e-ph coupling as a function of strain has been less studied. In this
work, the Kohn anomalies and the e-ph coupling in uniaxially strained graphene
along armchair (AC) and zigzag (ZZ) directions were studied by means of density
functional perturbation theory calculations. In addition to the phonon anomaly
at the transversal optical (TO) phonon branch in the K point for pristine
graphene, we found that uniaxial strain induces a discontinuity in the
frequency derivative of the longitudinal acoustic (LA) phonon branch. This
behavior corresponds to the emergence of a Kohn anomaly, as a consequence of a
strain-enhanced e-ph coupling. Thus, the present results for uniaxially
strained graphene contrast with the commonly assumed view that the e-ph
coupling around the K point is only present in the TO phonon branch.
