Surface defect gap solitons in one-dimensional dual-frequency lattices

We study the surface defect gap solitons in an interface between adefect of one-dimensional dual-frequency lattices and the uniformmedia. Some unique properties are revealed that such lattices canbroaden the region of semi-finite gap, and the semi-finite gapexists not only in the positive and zero defects but also in thenegative defect; unlike in the regular lattices, the semi-finite gapexists in the positive and zero defects but does not exist in thenegative defect. In particular, stable solitons exist almost in thewhole semi-finite gap for the positive and zero defects. Theseproperties are different from other lattices with defects. Inaddition, it is found that the existence of surface dual-frequencylattice solitons does not need a threshold power.