Ground State Properties of Antiferromagnetic Chains with Unrestricted Spin: Integer Spin Chains as Realisations of the O(3) Non-Linear Sigma Model

Understand

A continuum limit treatment of planar spin chains with arbitrary S is presented.

• The difference between integer and half-integer spins is emphasised.
• While isotropic half-integer spin chains are gapless,and have power-law decay of correlations at T = 0 with exponent eta = 1, integer spin systems have a singlet ground state with a gap for S=1 excitations and exponential decay of correlations.
• The easy-plane to easy-axis transition is described.