One-dimensional spin-liquid without magnon excitations

TL;DR

This paper demonstrates that strong four-spin interactions in a spin-1/2 ladder induce a dimerized phase with unique correlation functions, lacking magnon excitations, contrasting with the Haldane phase.

Contribution

It reveals how four-spin interactions can cause dimerization in spin ladders, leading to phases with distinct dynamical properties despite similar thermodynamic behavior.

Findings

Dimerization occurs due to strong four-spin interactions.

Dimerized phase lacks single magnon excitations.

Dynamical susceptibility shows a two-particle threshold.

Abstract

It is shown that a sufficiently strong four-spin interaction in the spin-1/2 spin ladder can cause dimerization. Such interaction can be generated either by phonons or (in the doped state) by the conventional Coulomb repulsion between the holes. The dimerized phases are thermodynamically undistinguishable from the Haldane phase, but have dramatically different correlation functions: the dynamical magnetic susceptibility, instead of displaying a sharp single magnon peak near $q = \pi$, shows only a two-particle threshold separated from the ground state by a gap.