X-Ray Scattering Study of Spin-Lattice Dimerization in a Quasi One-Dimensional Heisenberg Antiferromagnet.

摘要

X-ray measurements on the quasi one-dimensional Heisenberg antiferromagnet TTF-(Tetrathiafulvalenium-) CuS4C4(CF3)4 reveal a new crystallographic phase below T sub 0 = 11 K in which spin-1/2 TTF(+) units are paired. The temperature dependence of the order parameter below 11 K is accurately given by the BCS gap equation. Unexpectedly, the pairing is found along a diagonal direction in the b sub F - c sub F plane rather than along the molecular stacking axis c sub F. Furthermore, strong diffuse scattering dominates the x-ray cross section at the dimerization superlattice positions for temperatures as high as 225 K. (Author)