Non-d-wave Behavior Observed in Low-Temperature Specific Heat of Pr1.85Ce0.15CuO4.065

Abstract

Recently, possible evidence from the low-temperature specific heat (LTSH) for the lines of nodes in the superconducting order parameter of cuprate superconductors has attracted considerable attention and is still a controversial issue. To clarify this issue, N-type Pr1.85Ce0.15CuO4+δ samples have been prepared under different annealing conditions and investigated by means of X-ray diffraction and oxygen content analyses, and magnetic-susceptibility and low-temperature specific heat (LTSH) measurements. The values of oxygen content parameter δ for Pr1.85Ce0.15CuO4+δ are 0.161 and 0.065 for samples annealed in an Ar atmosphere and in vacuum, respectively. Pr1.85Ce0.15CuO4.161 shows clear evidence for an αT2 term at zero magnetic field in LTSH measurements, which is consistent with d-wave superconductivity. However, this behavior is not observed in Pr1.85Ce0.15CuO4.065. These results indicate that different heat treatments may change the oxygen content of Pr1.85Ce0.15CuO4+δ, resulting in the different behaviors observed in LTSH measurements. We also discuss the results of the LTSH measurements in La2-xSrxCuO4 (x=0.1, 0.16 and 0.22) to explain these behaviors observed in the LTSH data of Pr1.85Ce0.15CuO4+δ.