Observation of a Spin-Peierls Transition in a Heisenberg Antiferromagnetic Linear-Chain System

Abstract

Magnetic-susceptibility and EPR measurements are reported which provide the first unambiguous evidence for a spin-Peierls transition in a system of linear one-dimensional antiferromagnetic Heisenberg chains. The material studied is TTFCu${\mathrm{S}}_4$ ${\mathrm{C}}_4$ ${\left(\mathrm{C}{\mathrm{F}}_3\right)}_4$ (TFF stands for tetrathiafulvalinium). At 12 K, the spin-lattice system undergoes a second-order phase transition to a singlet ground state.