Massive and Massless Behavior in Dimerized Spin Ladders

TL;DR

This paper explores how specific interactions in dimerized spin-1/2 chains can lead to gapless excitations despite tendencies toward gapped phases, using analytical and numerical methods.

Contribution

It identifies conditions under which a gap vanishes in dimerized coupled spin chains, revealing the interplay of interchain coupling and dimerization.

Findings

Certain combinations of interchain and dimerization couplings produce massless spin excitations.

Different dimerization patterns influence the emergence of magnetization plateaus.

The study combines bosonization and Lanczos diagonalization techniques for analysis.

Abstract

We investigate the conditions under which a gap vanishes in the spectrum of dimerized coupled spin-1/2 chains by means of Abelian bosonization and Lanczos diagonalization techniques. Although both interchain ($J'$) and dimerization ($\delta$) couplings favor a gapful phase, it is shown that a suitable choice of these interactions yields massless spin excitations. We also discuss the influence of different arrays of relative dimerization on the appearance of non-trivial magnetization plateaus.