Magnetic Superstructure in the Two-Dimensional Quantum Antiferromagnet SrCu2(BO3)2
K. Kodama,1
M. Takigawa,1*
M. Horvati
,2
C. Berthier,23
H. Kageyama,1
Y. Ueda,1
S. Miyahara,14
F. Becca,4
F. Mila4
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.
1 Institute for Solid State Physics, University
of Tokyo, Kashiwa, Chiba 277-8581, Japan.
2 Grenoble
High Magnetic Field Laboratory, CNRS and MPI-FKF, 38042 Grenoble,
France.
3 Laboratoire de Spectrométrie
Physique, Université Joseph Fourier Grenoble I, 38402 St.-Martin
d'Hères, France.
4 Institut de Physique
Théorique, Université de Lausanne, CH-1015 Lausanne,
Switzerland.
*
To whom correspondence should be addressed. E-mail:
masashi{at}issp.u-tokyo.ac.jp
