CNR-INFM Laboratorio Regionale SUPERMAT, and Dipartimento di Fisica E.R. Caianiello, Università di Salerno, Baronissi (SA), Italy.
J Phys Condens Matter. 2010 Feb 3;22(4):045702. doi: 10.1088/0953-8984/22/4/045702. Epub 2010 Jan 12.
We have performed scanning tunneling spectroscopy and point contact spectroscopy measurements on the electron-doped superconductor Pr(1-x)LaCe(x)CuO(4-y) (x = 0.12, T(c) is approximately equal 25 K). We address the question of the symmetry of the order parameter and of the amplitude of the energy gap. We compare three possible scenarios, i.e. isotropic s-wave, 'anisotropic' s-wave, and d-wave. Evidence for a d-wave symmetry of the order parameter is given. From the temperature evolution of the dI/dV versus V characteristics we extract a BCS-like temperature dependence of the superconducting energy gap Δ. Despite the variety of measured spectra we give a consistent explanation for the whole set of data, indicating Δ = (3.6 ± 0.2) meV and a ratio 2Δ/K(B)T(C) is approximately equal 3.5 ±0.2. In particular, point contact characteristics showing gap-like features at higher voltages have been interpreted by considering the formation of an intergrain Josephson junction in series with the point contact junction. Further confirmation of the correctness of the model is given by the behavior of the critical current of the intergrain Josephson junction versus temperature which follows the Ambegaokar-Baratoff behavior.
我们对电子掺杂超导体 Pr(1-x)LaCe(x)CuO(4-y)（x = 0.12，T(c)约为 25 K）进行了扫描隧道谱和点接触谱测量。我们研究了序参量的对称性和能隙幅度的问题。我们比较了三种可能的情况，即各向同性 s 波、“各向异性”s 波和 d 波。给出了序参量具有 d 波对称性的证据。从 dI/dV 与 V 的温度演化特性中，我们提取出超导能隙 Δ 的 BCS 型温度依赖性。尽管测量的谱线种类繁多，但我们对整个数据集给出了一致的解释，表明 Δ = (3.6 ± 0.2) meV，且 2Δ/K(B)T(C)约等于 3.5 ±0.2。特别是，通过考虑与点接触结串联的晶粒间约瑟夫森结的形成，解释了在较高电压下具有能隙特征的点接触特性。晶粒间约瑟夫森结的临界电流随温度的变化遵循 Ambegaokar-Baratoff 行为，这进一步证实了该模型的正确性。
