Series expansion analysis of a tetrahedral cluster spin chain

Using analytical series expansion by continuous unitary transformations we study the magnetic properties of a frustrated tetrahedral spin-<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\frac{1}{2}$</EquationSource> </InlineEquation> chain. Starting from the limit of isolated tetrahedra we analyze the evolution of the ground state energy and the elementary triplet dispersion as a function of the inter-tetrahedral coupling. The quantum phase diagram is evaluated and is shown to incorporate a singlet product, a dimer, and a Haldane phase. Comparison of our results with those from several other techniques, such as density matrix renormalization group, exact diagonalization, bond-operator theory and other numerical series expansion are provided and convincing agreement is found. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2006