  The properties of the strongly interacting edge states of two dimensional
topological insulators in the presence of two particle backscattering are
investigated. We find an anomalous behavior of the density-density correlation
functions, which show oscillations that are neither of Friedel nor of Wigner
type: they instead represent a Wigner crystal of fermions of fractional charge
e/2, with e the electron charge. By studying the Fermi operator, we show that
the state characterized by such fractional oscillations still bears the
signatures of spin momentum locking. Finally, we compare the spin-spin
correlation functions and the density-density correlation functions to argue
that the fractional Wigner crystal is characterized by a non trivial spin
texture.
