Anomalous change in the field dependence of the electronic specific heat of an electron-doped cuprate superconductor

We present specific heat measurements on Pr2-xCexCuO4-delta single crystals which show an unexpected change in the field dependence of the electronic specific heat (C-el) from linear at T=2 K to nonlinear at Tgreater than or equal to3 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 Tgreater than or equal to3 K to gapped (e.g., s wave) at T=2 K. Such a phase transition could be an explanation for the previous conflicting experimental results on the pairing symmetry in the electron-doped cuprates.