Darboux transformation and dark soliton solution for the defocusing Sasa-Satsuma equation

In this Letter, the Darboux transformation is first applied to the defocusing Sasa-Satsuma equation which describes the propagation dynamics of ultrashort light pulses in the normal dispersion regime of optical fibers. The N-fold iterative transformation is expressed in terms of the determinants. This transformation enables us to construct explicit analytical dark soliton solutions from non-vanishing background. In illustration, the single-dark soliton solution is presented from the once-iterated formula.