Observation of Ultraslow Group Velocity of Light in a Solid
  We report ultraslow group velocities of light in a solid. Light speeds as slow as 45 m/s were observed, corresponding to a group delay of 66 ms in a 3-mm thick crystal. Reduction of the group velocity is accomplished by using a sharp spectral feature in absorption and dispersion, produced by a Raman excited spin coherence in an optically dense Pr doped Y2SiO5 crystal. 
A.V. Turukhin, V.S. Sudarshanam, M. S. Shahriar, J. A. Musser, and   P.R. Hemmer