Phase diagram of three-leg spin ladder

Abstract

The spin- spin ladder with single-ion anisotropy and bond alternation is analysed using the bosonization technique and other methods. Our argument is mainly devoted to the case of three legs. Combining the renormalization group analysis with the results of the strong-coupling limits, we predict that the translationally invariant model is gapless regardless of the single-ion anisotropy and described by the c = 1 conformal field theory (CFT). It is also argued that the response to the bond alternation is quite different according to the sign of the interchain coupling.