  We show that the photonic angular momentum states (AMSs) in metamaterials can
be utilized to achieve slow light. The photonic AMS possesses a helical phase,
the orbital-angular-momentum degree of freedom in photons. Unlike the
traditional slow-light schemes in metamaterials by using orthogonal
polarizations, the photonic AMSs are dipole forbidden for all polarizations of
free-space radiation due to the existence of helical phase. Numerical
simulation for a metamaterial design proves the feasibility of this scheme, in
which the indirectly excitation of dark photonic AMSs burns some transmission
dips in the otherwise high transmission window. With the unique merits of dark
photonic AMSs, this slow light scheme can realize a high group index $n_g$
greater than $\sim500$.
