Non-d-wave Behavior Observed in Low-Temperature Specific Heat of Pr_1.85Ce_0.15CuO_4.065

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 Pr 1.85 Ce 0.15 CuO 4+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 Pr 1.85 Ce 0.15 CuO 4+δ are 0.161 and 0.065 for samples annealed in an Ar atmosphere and in vacuum, respectively. Pr 1.85 Ce 0.15 CuO 4.161 shows clear evidence for an α T 2 term at zero magnetic field in LTSH measurements, which is consistent with d -wave superconductivity. However, this behavior is not observed in Pr 1.85 Ce 0.15 CuO 4.065 . These results indicate that different heat treatments may change the oxygen content of Pr 1.85 Ce 0.15 CuO 4+δ , resulting in the different behaviors observed in LTSH measurements. We also discuss the results of the LTSH measurements in La 2- x Sr x CuO 4 ( x =0.1, 0.16 and 0.22) to explain these behaviors observed in the LTSH data of Pr 1.85 Ce 0.15 CuO 4+δ .