  We consider two-component "spinor" slow light in an ensemble of atoms
coherently driven by two pairs of counterpropagating control laser fields in a
double tripod-type linkage scheme. We derive an equation of motion for the
spinor slow light (SSL) representing an effective Dirac equation for a massive
particle with the mass determined by the two-photon detuning. By changing the
detuning the atomic medium acts as a photonic crystal with a controllable band
gap. If the frequency of the incident probe light lies within the band gap, the
light tunnels through the sample. For frequencies outside the band gap, the
transmission probability oscillates with increasing length of the sample. In
both cases the reflection takes place into the complementary mode of the probe
field. We investigate the influence of the finite excited state lifetime on the
transmission and reflection coefficients of the probe light. We discuss
possible experimental implementations of the SSL using alkali atoms such as
Rubidium or Sodium.
