Date of Original Version
The spin-Peierls transition is considered as a progressive spin-lattice dimerization occurring below a transition temperature in a system of one-dimensional antiferromagnetic Heisenberg chains. In the simplest theories, the transition is second order and the ground state is a singlet with a magnetic gap. The historical origins and theoretical development of the concept are examined. Magnetic susceptibility and EPR measurements on the π-donor-acceptor compounds TTF·MS4C4(CF3)4 (M=Cu, Au; TTF is tetrathiafulvalene) are reported. These compounds exhibit clearly the characteristics of the spin-Peierls transition in reasonably good agreement with a mean-field theory. The susceptibility of each compound has a broad maximum near 50 K, while the transitions occur at 12 and 2.1 K for M=Cu and Au, respectively. EPR linewidth observations over a broad temperature range are examined. Areas for further experimental and theoretical work are indicated, and a critical comparison is made of related observations on other materials.
I.S. Jacobs, J.W. Bray, H.R. Hart, L.V. Interrrante, J.S. Kasper, G.D. Watkins, D.E. Prober, and Jill. C. Bonner, Phys. Rev. B 14, 3036 (1976). Available at: http://dx.doi.org/10.1103/PhysRevB.14.3036