Spin gaps in coupledt-Jladders

Abstract

Spin gaps in coupled t-J ladders are investigated by exact diagonalization of small clusters up to 4×8 sites. At half-filling, the numerical results for the triplet excitation spectrum are in very good agreement with a second-order perturbation expansion in terms of small interladder and intraladder exchange couplings between rungs (J/J’J, roughly half of the single-ladder spin gap. When the system is hole doped, bonding and antibonding bound pairs of holes can propagate coherently along the chains and the spin gap remains finite.