arXiv subjects
Publications and source records attributed to M. Roncaglia.
We study the ground state of the 4-leg spin ladder using a dimer-RVB ansatz and the Lanczos method. Besides the well known resonance mechanism between valence bond configurations we find novel interference effects among nearby resonances.
We derive a path-integral expression for the effective action in the continuum limit of an AFM Heisenberg spin ladder with an arbitrary number of legs. The map is onto an $O(3)$ nonlinear $σ$-model (NL$σ$M) with the addition of a topological term that is effective only for odd-legged ladders and half-odd integer spins. We derive the parameters of the effective NL$σ$M and the behaviour of the spin gap for the case of even-legged ladders.