Figure 3: Magnetic field dependence of the specific heat in YBa2Cu3O6.54.
ΔCp(H, T)/T=Cp(H, T)/T−Cp(0, T)/T initially increases almost linearly with field due to the increase of the number of vortices in the mixed state and flattens off for large magnetic fields. Solid lines correspond to the modulation technique results (at the indicated temperatures) and the solid (blue) squares at 10 K have been obtained using a relaxation technique. The (purple) squares at 3 K correspond to the difference 
between data obtained for both field orientations (see text for details). The vertical dotted lines mark the position of the irreversibility line deduced from magnetic measurements (see Fig. 4) corresponding to the solid/liquid transition line. As shown, the specific heat anomaly clearly lies in the vortex liquid and is therefore not related to the melting of the vortex solid. The HCp values corresponding to the maximum of Cp (or onset of saturation al low temperature) have been reported in Fig. 2 (solid (red) circles). The error bars are systematic uncertainties obtained from the calibration measurements performed on ultrapure copper.
