Year: 2002
Type: article
Abstract: Recent investigations of the two-dimensional spin-1/2 checkerboard lattice favor a valence bond crystal with long-range quadrumer order [J.-B. Fouet, M. Mambrini, P. Sindzingre, and C. Lhuillier, cond-mat/0108070 (unpublished)]. Starting from the limit of isolated quadrumers, we perform a complementary analysis of the evolution of the spectrum as a function of the interquadrumer coupling j using both exact diagonalization (ED) and series expansion (SE) by continuous unitary transformation. We compute (i) the ground-state energy, (ii) the elementary triplet excitations, and (iii) singlet excitations on finite systems and find very good agreement between SE and ED. In the thermodynamic limit we find a ground-state energy substantially lower than that documented in the literature. The elementary triplet excitation is shown to be gapped and almost dispersionless, whereas the singlet sector contains strongly dispersive modes. Evidence is presented for the low energy singlet excitations in the spin gap in the vicinity of $j=1$ to result from a large downward renormalization of local high-energy states.
Authors: Wolfram Brenig, Andreas Honecker
Institution: Technische Universität Braunschweig
Language: English
Subfield: Condensed Matter Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2035326523