  Elementary excitations in condensed matter capture the complex many-body
dynamics of interacting basic entities in a simple quasiparticle picture. In
magnetic systems the most established quasiparticles are magnons, collective
excitations that reside in ordered spin structures, and spinons, their
fractional counterparts that emerge in disordered, yet correlated spin states.
Here we report on the discovery of elementary excitation inherent to
spin-stripe order that represents a bound state of two phason quasiparticles,
resulting in a wiggling-like motion of the magnetic moments. We observe these
excitations, which we dub "wigglons", in the frustrated zigzag spin-1/2 chain
compound $\beta$-TeVO$_4$, where they give rise to unusual low-frequency spin
dynamics in the spin-stripe phase. This result provides insights into the
stripe physics of strongly-correlated electron systems.
