Thermodynamic properties of the incommensurate phase of CuGeO3

We present high-resolution measurements of the specific heat and the thermal expansion of the inorganic spin-Peierls cuprate CuGeO3 in a magnetic field of 16 T. At the transition from the incommensurate to the uniform phase both quantities show pronounced anomalies, which allow us to derive the uniaxial pressure dependences of the transition temperature. In high magnetic fields the specific heat is dominated by magnetic excitations and follows a T-3 law at low temperatures. The thermal expansion measurements show the occurrence of spontaneous strains along all three lattice constants and yield high-resolution measurements of the temperature dependence of the incommensurate structural distortion. The sizes of the spontaneous strains in the incommensurate phase are significantly reduced, but both their anisotropy as well as their temperature dependences are very similar to those in zero field.