On the energy spectrum of a spin lattice formed by a finite number of coupled spin-1/2 XY chains

We studied the energy spectrum of a spin lattice formed by m XY spin-1/2 chains with Ising inter-chain coupling. For strong ferromagnetic coupling we found that the lowest-energy states for non-zero numbers of inverted spins on each XY chain have n-magnon bound character if n = ml − 1, where l = 2, 3,.... For a spin tube formed by three XY chains with strong ferromagnetic inter-chain coupling, the lowest-energy states are described by the XXZ spin-1/2 chain model with antiferromagnetic coupling.