SPECIFIC-HEAT OF QUANTUM-SPIN CHAINS - APPLICATION TO (C6H11NH3)CUBR3 AND (C6H11NH3)CUCL3

A real-space renormalization-group (RSRG) approach and numerical calculations are applied in order to study the specific heat of (C6H11NH3)CuBr3 and (C6H11NH3)CuCl3, which are built up of the ferromagnetic spin-1/2 quantum chains and are described by anisotropic Heisenberg models. As to the RSRG approach, our previous zero-field easy-plane calculations are extended to the XYZ model in the presence of a magnetic field, and qualitative agreement with experiment is found, especially in the appearance of the soliton peaks in the in-plane excess specific heat. Imposing free boundary conditions, the finite-size numerical results are applied to chains with length N12 and extrapolated for 1/N0. Good convergence for most temperatures is found, and agreement with experiment is concluded. © 1990 The American Physical Society.