Abstract By using the Bogoliubov–de Gennes equation and the Nambu spinor Greens function approach, we have theoretically studied the dc Josephson current and the coupling phase state of superconductor/ferromagnet/superconductor (SC/FM/SC) junctions, where the FM is of weak ferromagnetism. From the behavior of the temperature-dependent dc Josephson current ( I c ), we confirm that such SC/FM/SC junction may change from 0-phase to π -phase state with increasing the temperature ( T ), for particular parameters of the thickness and the strength of ferromagnetism of the FM interlayer. We attribute such changement to an extra phase difference between the two SCs. The results are qualitatively consistent with an experiment [Phys. Rev. Lett. 86 (2001) 2427], which shows a sharp cusp structure on the I c − T curves of Nb/Cu 0.48 Ni 0.52 /Nb junction for specific thickness of the Cu 0.48 Ni 0.52 , indicating the junction changes from 0-phase state at high temperatures to π -phase state at low temperatures.

中文翻译：

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超导体/铁磁体/超导体结中的约瑟夫森电流

摘要 通过使用 Bogoliubov-de Gennes 方程和 Nambu Spinor Greens 函数方法，我们从理论上研究了直流约瑟夫森电流和超导体/铁磁体/超导体 (SC/FM/SC) 结的耦合相位状态，其中 FM 为弱铁磁性。根据温度相关的直流约瑟夫森电流 (Ic) 的行为，我们确认这种 SC/FM/SC 结可能会随着温度 (T) 的增加而从 0 相变为 π 相状态，对于FM 夹层的厚度和铁磁性强度。我们将这种变化归因于两个 SC 之间的额外相位差。结果与实验 [Phys. 牧师莱特。86 (2001) 2427]，显示了 Nb/Cu 0.48 Ni 0 的 I c - T 曲线上的尖尖结构。