NiCl2-4SC(NH2)2 (known as DTN) is a spin-1 material with a strong single-ion anisotropy that is regarded as a new candidate for Bose-Einstein condensation (BEC) of spin degrees of freedom. We present a systematic study of the low-energy excitation spectrum of DTN in the field-induced magnetically ordered phase by means of high-field electron spin resonance measurements at temperatures down to 0.45 K. We argue that two gapped modes observed in the experiment can be consistently interpreted within a four-sublattice antiferromagnet model with a finite interaction between two tetragonal subsystems and unbroken axial symmetry. The latter is crucial for the interpretation of the field-induced ordering in DTN in terms of BEC.
@article{arxiv.0802.0352,
title = {Spin Dynamics of $Ni Cl_2-4SC(NH_2)_2$ in the Field-Induced Ordered Phase},
author = {S. A. Zvyagin and J. Wosnitza and A. K. Kolezhuk and V. S. Zapf and M. Jaime and A. Paduan-Filho and V. N. Glazkov and S. S. Sosin and A. I. Smirnov},
journal= {arXiv preprint arXiv:0802.0352},
year = {2009}
}