Next: Structural investigations [#!MonctonPRL77!#,#!vanBodegomPRB81!#]
Up: 6.1 Introduction
Previous: 6.1.1 Theories
The spin Peierls transition was observed experimentally in
the 1970's, with organic materials such as, TTF-CuBDT, TTF-AuBDT
[127,128] and MEM-(TCNQ)2 .
These materials show a structural transition at relatively high
temperatures (=240 K for TTF-CuBDT and 340 K for
MEM-(TCNQ)2), so that a one dimensional chain structure is prepared.
The S=1/2 spins are held by a lone-pair on a molecule (TTF+ and
In these materials, the spin Peierls transition was identified with an
exponential drop of susceptibility below (11 K for TTF-CuBDT
[127,128] and 18 K for MEM-(TCNQ)2
). Contrary to an antiferromagnetic Néel order,
the drop of susceptibility is isotropic, suggesting a spin singlet
formation. In the following, other experimental signatures of spin
Peierls transition are introduced.