Gapless singlet modes in the kagomé strips: A study through density-matrix-renormalization group and strong-coupling analysis

摘要: Recently, Azaria et al. [Phys. Rev. Lett. 81, 1694 (1998)] have studied strips of the kagom\'e lattice in weak-coupling limit, where they consist two spin-half chains on outside weakly coupled to an array half-integer spins middle. Using a number mappings, arrived at interesting result that this system all spin excitations are gapped but there gapless spinless modes. Here, we study these limit interchain couplings comparable coupling middle by density-matrix-renormalization group and strong-coupling analysis. In when middle-spin dominates, five-spins unit-cell reduce single $S=3/2$ spin, overall has well known excitations. We phase transition from phase. also carry out analysis away five-spin blocks four degenerate ground states with $S=1/2,$ which can be thought as pseudospin degrees freedom. A numerical strong model suggests finite gap.