Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders

TL;DR

This study investigates magnon excitations in a quasi-one-dimensional spin ladder compound undergoing Bose-Einstein condensation, revealing both similarities and key differences in excitation behavior compared to 3D quantum magnets.

Contribution

It provides the first detailed neutron scattering analysis of magnon excitations in a coupled spin ladder system in the BEC regime, highlighting unique excitation dynamics.

Findings

Detection of commensurate long-range order and Goldstone mode

Observation of drastic collapse of magnon bandwidth beyond transition

Differences in behavior of massive magnon branches compared to 3D magnets

Abstract

The weakly coupled quasi-one-dimensional spin ladder compound (CH$_3$)$_2$CHNH$_3$CuCl$_3$ is studied by neutron scattering in magnetic fields exceeding the critical field of Bose-Einstein condensation of magnons. Commensurate long-range order and the associated Goldstone mode are detected and found to be similar to those in a reference 3D quantum magnet. However, for the upper two massive magnon branches the observed behavior is totally different, culminating in a drastic collapse of excitation bandwidth beyond the transition point.