The Spin-Peierls Transition

The spin-Peierls transition is an unusual kind of magnetoelastic transition occurring (at least in in its simplest form) in a very limited number of quasi-one-dimensional insulating systems. It was predicted theoretically almost two decades ago, in the general context of physical chemistry and the properties of certain organic free radicals in particular. The first clear-cut experimental realization was not discovered until 1975.1,2 The discovery was made in the wake of a high level of interest which developed among physicists in the properties of quasi-one-dimensional organic conductors (organic metals), of which (tetrathiafulvalene)(7,7,8,8-tetracyano-p-quinodimethane), (TTF)(TCNQ), remains the best-known example. Typical programs proceeded by synthesis followed by conductivity measurements, and low-conductivity samples were routinely discarded. The program followed at General Electric involved combining organic donors (e.g., TTF) with metallo-organic planar acceptors called metal bisdithiolene (BDT) complexes, MBDT, where M is a metal atom, such as Cu, Au, or Pt. In the case of (TTF)(CuBDT), the system was found to be an excellent insulator; however, magnetization studies suggested low-dimensional behavior (quasi-one-dimensional behavior) with curious properties.