Optical absorption of spin ladders

TL;DR

This paper develops a theoretical model for phonon-assisted optical two-magnon absorption in two-leg spin ladders, revealing collective excitations and a distinct signature of the singlet state in the optical spectrum.

Contribution

It introduces a new theoretical approach focusing on the strong intra-rung-coupling limit to identify collective spin excitations in spin ladders.

Findings

Collective excitations of total spin S=0, 1, 2 exist outside the two-magnon continuum.

The singlet collective state produces a clear signature in the optical spectrum.

The theory explains features of phonon-assisted optical absorption in spin ladders.

Abstract

We present a theory of phonon-assisted optical two-magnon absorption in two-leg spin-ladders. Based on the strong intra-rung-coupling limit we show that collective excitations of total spin S=0, 1 and 2 exist outside of the two-magnon continuum. It is demonstrated that the singlet collective state has a clear signature in the optical spectrum.