Longitudinal SDW order in a quasi-1D Ising-like quantum antiferromagnet
  From neutron diffraction measurements on a quasi-1D Ising-like Co$^{\rm 2+}$ spin compound BaCo$_{\rm 2}$V$_{\rm 2}$O$_{\rm 8}$, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the N{\' e}el-type ordering, which is expected for the classical system, and is caused by quantum fluctuation inherent in the quantum spin chain. A Tomonaga-Luttinger liquid (TLL) nature characteristic of the gapless quantum 1D system is responsible for the realization of the incommensurate ordering. 
S. Kimura, M. Matsuda, T. Masuda, S. Hondo, K. Kaneko, N. Metoki, M.   Hagiwara, T. Takeuchi, K. Okunishi, Z. He, K. Kindo, ...