Observation of Phase Transition with Lattice Distortion in the Low-dimensional Quantum Spin System TiOBr by Synchrotron X-ray Diffraction —Evidence of Spin-Peierls Transition?—

Abstract

Here, we report on the direct observation of lattice distortion in the new quasi-one-dimensional spin system TiOBr by X-ray diffraction experiment using synchrotoron radiation. By comparing the crystal structure between TiOBr and TiOCl, the difference in b-axis length was considered to play a key role in determining the physical properties of both systems. Using a single crystal sample of TiOBr, superlattice reflections were observed at (0,1.5,0) and (0,2.5,0). The temperature dependence of the superlattice reflections implied the first-order transition at T_c1=27 K. We discussed the phase transition and analyzed the data using a simple dimerization model.