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キーワード:
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要旨:
We report the observation of magnetic superstructure in a
magnetization plateau state of SrCu2(BO3)(2), a frustrated
quasi two-dimensional quantum spin system. The Cu and B nuclear
magnetic resonance (NMR) spectra at 35 millikelvin indicate an
apparently discontinuous phase transition from uniform
magnetization to a modulated superstructure near 27 tesla,
above which a magnetization plateau at 1/8 of the full
saturation has been observed. Comparison of the Cu NMR spectrum
and the theoretical analysis of a Heisenberg spin model
demonstrates the crystallization of itinerant triplets in the
plateau phase within a large rhomboid unit cell (16 spins per
layer) showing oscillations of the spin polarization. Thus, we
are now in possession of an interesting model system to study a
localization transition of strongly interacting quantum
particles.
