Magnetic excitations in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and Dzyaloshinskii-Moriya interactions that exhibits a field-induced spin gap, are probed by means of pulsed-field electron spin resonance spectroscopy. In particular, we report on a minimum of the gap in the vicinity of the saturation field Hsat=48.5 T associated with a transition from the sine-Gordon region (with soliton-breather elementary excitations) to a spin-polarized state (with magnon excitations). This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG investigation of the spin-1/2 Heisenberg chain with a staggered transverse field.
@article{arxiv.1010.6141,
title = {Field-Induced Gap in a Quantum Spin-1/2 Chain in a Strong Magnetic Field},
author = {S. A. Zvyagin and E. Čižmár and M. Ozerov and J. Wosnitza and R. Feyerherm and S. R. Manmana and F. Mila},
journal= {arXiv preprint arXiv:1010.6141},
year = {2011}
}