  In our previous work [Phys. Rev. Lett. 103, 103602 (2009)], we found that
repulsive Casimir forces could be realized by using chiral metamaterials if the
chirality is strong enough. In this work, we check four different chiral
metamaterial designs (i.e., Twisted-Rosettes, Twisted-Crosswires, Four-U-SRRs,
and Conjugate-Swastikas) and find that the designs of Four-U-SRRs and
Conjugate-Swastikas are the most promising candidates to realize repulsive
Casimir force because of their large chirality and the small ratio of structure
length scale to resonance wavelength.
