The temperature dependence of the spin - Peierls energy gap in

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Abstract
We have studied the temperature dependence of the spin - Peierls (SP) energy gap in a single crystal of using cold neutrons. Our measurements enable us to examine the scaling relationship between the magnitude of the SP gap and the intensity of the structural superlattice peak in the vicinity of the transition temperature (). We also discuss our data in the context of recent numerical calculations for which different scaling laws are obtained depending on the magnitude of the intrachain next-nearest-neighbour interaction in a Heisenberg spin-chain Hamiltonian. The consequence of two-dimensional correlations and the possible existence above of a second low-lying energy gap due to frustration are considered.