  The Raman selection rules arise from the crystal symmetry and then determine
the Raman activity and polarization of scattered phonon modes. However, these
selection rules can be broken in resonant process due to the strong
electron-phonon coupling effect. Here we reported the observation of breakdown
of Raman selection rules in few-layer WS$_2$ by using resonant Raman scattering
with dark A exciton. In this case, not only the infrared active modes and
backscattering forbidden modes are observed, but the intensities of all
observed phonon modes become strongest under paralleled-polarization and
independent on the Raman tensors of phonons. We attributed this phenomenon to
the interaction between dark A exciton and the scatted phonon, the so-called
intraband Fr\"{o}hlich interaction, where the Raman scattering possibility is
totally determined by the symmetry of exciton rather than the phonons due to
strong electron-phonon coupling. Our results not only can be used to easily
detect the optical forbidden excitonic and phononic states but also provide a
possible way to manipulate optical transitions between electronic levels.

Materials Science;Strongly Correlated Electrons;Optics