Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK.
Nat Commun. 2014;5:3340. doi: 10.1038/ncomms4340.
Higher harmonics in current-phase relations of Josephson Junctions are predicted to be observed when the first harmonic is suppressed. Conventional theoretical models predict higher harmonics to be extremely sensitive to changes in barrier thickness, temperature, and so on. Here we report experiments with Josephson junctions incorporating a spin-dependent tunnelling barrier, revealing a current-phase relation for highly spin polarized barriers that is purely second harmonic in nature and is insensitive to changes in barrier thickness. This observation implies that the standard theory of Cooper pair transport through tunnelling barriers is not applicable for spin-dependent tunnelling barriers.
当抑制第一谐波时，预计会观察到约瑟夫森结电流相位关系中的高次谐波。传统的理论模型预测高次谐波对势垒厚度、温度等的变化极其敏感。在这里，我们报告了包含自旋相关隧道势垒的约瑟夫森结实验，揭示了对于高度自旋极化势垒的电流相位关系，其本质上是纯二次谐波，并且不受势垒厚度变化的影响。这一观察结果表明，通过隧道势垒的库珀对输运的标准理论不适用于自旋相关隧道势垒。
