Observation of pinning mode in Wigner solid of 1/3 fractional quantum Hall excitations

We report the observation of a resonance in the microwave spectra of the real diagonal conductivities of a two-dimensional electron system within a range of ~ +- .0.015 $ from filling factor $ u=1/3$. The resonance is remarkably similar to resonances previously observed near integer $ u$, and is interpreted as the collective pinning mode of a disorder-pinned Wigner solid phase of $e/3$-charged carriers .