GIANT ANOMALIES OF THE THERMAL-EXPANSION AT THE SPIN-PEIERLS TRANSITION IN CUGEO3

The thermal-expansion coefficients α of the spin-Peierls cuprate CuGeO3 have been measured along the three orthorhombic directions using a high-resolution capacitance dilatometer. We observe giant, strongly anisotropic anomalies at the spin-Peierls transition temperature (TSP) and spontaneous strains along all three crystal axes below TSP. From the jumps of α and the specific heat we estimate large uniaxial pressure dependencies of TSP, in particular for pressure applied perpendicular to the one-dimensional Cu2+ chains. In addition, we observe an anomalous temperature dependence of the thermal expansion above the transition showing a striking similarity to that of the magnetic susceptibility. © 1995 The American Physical Society.