Quantum chiral phases in frustrated easy-plane spin chains

The phase diagram of antiferromagnetic spin-S chain with XY-type anisotropy and frustrating next-nearest-neighbor interaction is studied in the limit of large integer S with the help of a field-theoretical approach. It is sho wn that the existence of gapless and gapped chiral phases found in recent n umerical studies [M. Kaburagi er nl., J. Phys. Sec. Jpn. 68, 3185 (1999); T . Hikihara et al., J. Phys. Sec. Jpn. 69, 259 (2000)] is not specific for S =1, but is rather a generic large-g feature. Estimates for the correspondin g transition boundaries are obtained, and a sketch of the typical phase dia gram is presented. Tt is also shown that frustration stabilizes the Haldane phase against the variation of the anisotropy.