  The realization of artificial gauge fields and spin-orbit coupling for
ultra-cold quantum gases promises new insight into paradigm solid state
systems. Here we experimentally probe the dispersion relation of a spin-orbit
coupled Bose-Einstein condensate loaded into a translating optical lattice by
observing its dynamical stability, and develop an effective band structure that
provides a theoretical understanding of the locations of the band edges. This
system presents exciting new opportunities for engineering condensed-matter
analogs using the flexible toolbox of ultra-cold quantum gases.
