Excitations and Possible Bound States in the S=1/2 Alternating Chain Compound (VO)2P2O7

TL;DR

This study uses inelastic neutron scattering to reveal that (VO)2P2O7 is an alternating spin chain with bound magnon states, challenging previous models of it as a two-leg ladder.

Contribution

The paper demonstrates that (VO)2P2O7 is better described as an alternating spin chain and identifies potential bound magnon states, providing new insights into its magnetic excitations.

Findings

(VO)2P2O7 is an alternating spin chain along the b-direction.

A second magnetic excitation suggests the presence of bound magnon states.

Numerical results support the existence of two-magnon bound modes.

Abstract

Magnetic excitations in an array of (VO)2P2O7 single crystals have been measured using inelastic neutron scattering. Until now, (VO)2P2O7 has been thought of as a two-leg antiferromagnetic Heisenberg spin ladder with chains running in the a-direction. The present results show unequivocally that (VO)2P2O7 is best described as an alternating spin-chain directed along the crystallographic b-direction. In addition to the expected magnon with magnetic zone-center energy gap DE = 3.1$ meV, a second excitation is observed at an energy just below 2DE. The higher mode may be a triplet two-magnon bound state. Numerical results in support of bound modes are presented.