Longitudinal spin density wave order in a quasi-1D Ising-like quantum antiferromagnet

Kimura, Shojiro*; Matsuda, Masaaki; Masuda, Takatsugu*; Hondo, Suguru*; Kaneko, Koji   ; Metoki, Naoto   ; Hagiwara, Masayuki*; Takeuchi, Tetsuya*; Okunishi, Koichi*; He, Z.*; Kindo, Koichi*; Taniyama, Tomoyasu*; Ito, Mitsuru*

From neutron diffraction measurements on a quasi-1D Ising-like Co spin compound BaCoVO, we observed an appearance of a novel type of incommensurate ordering in magnetic fields. This ordering is essentially different from the Nel-type ordering, which is expected for the classical system, and the peculiar spin structure 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.