We present specific heat measurements on ${\mathrm{P}\mathrm{r}}_{2-x}{\mathrm{C}\mathrm{e}}_x{\mathrm{C}\mathrm{u}\mathrm{O}}_{4-\delta }$ single crystals which show an unexpected change in the field dependence of the electronic specific heat ($C_{\mathrm{e}\mathrm{l}}$) from linear at $T=2\mathrm{K}$ to nonlinear at $T\ge 3\mathrm{K}$. We consider several possible explanations for this change and propose, as a possible interpretation, a phase transition in the symmetry of the order parameter from nodal (e.g., $d$ wave) at $T\ge 3\mathrm{K}$ to gapped (e.g., $s$ wave) at $T=2\mathrm{K}$. Such a phase transition could be an explanation for the previous conflicting experimental results on the pairing symmetry in the electron-doped cuprates.

• Received 30 January 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.067001