The fate of spinons in spontaneously dimerised spin-1/2 ladders

Abstract

We study a weakly coupled, frustrated two-leg spin-1/2 Heisenberg ladder. For vanishing coupling between the chains, elementary excitations are deconfined, gapless spin-1/2 objects called spinons. We investigate the fate of spinons for the case of a weak interchain interaction. We show that despite a drastic change in ground state, which becomes spontaneously dimerised, spinons survive as elementary excitations but acquire a spectral gap. We furthermore determine the exact dynamical structure factor for several values of momentum transfer.

8 pages of revtex, 7 figures; discussion of physical picture for ground state and excitations in the "twistless" ladder expanded, version to appear in Phys Rev B