  We study the polar collective dynamics of Janus colloidal particles fueled by
an AC electric field. When the density is high enough, the polar interactions
between the particles induce a polar orientationally ordered state which
exhibits features reminiscent of the Vicsek model such as true long-range order
and giant number fluctuations. Independent measurements of the polarity and
velocity at the single particle level allowed us to investigate the single
particle dynamics within the ordered state. We discovered
theoretically-unaddressed statistical properties of the ordered state such as
the asymmetric relation of polarity and velocity, enhanced rotational diffusion
stronger than in the disordered state, and an algebraic auto-correlation of the
polarity. Our experimental findings, at the crossroad of the Vicsek physics and
the Active Brownian Particles physics, shed light on the so-far-unexplored
physics arising from the interplay between the polarity and the velocity.
