Reversing the direction of the supercurrent in a controllable Josephson junction
Reversing the direction of the supercurrent in a controllable Josephson junction
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DOI：
10.1038/16204
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发表时间：
1999-01-07
期刊：
影响因子：
64.8
通讯作者：
Klapwijk, TM
中科院分区：
文献类型：
--
作者：
Baselmans, JJA;Morpurgo, AF;Klapwijk, TM
当两个超导体通过弱链接连接时，就会产生超电流，其大小取决于超导体宏观量子相的差异。这一现象是由Josephson(1)发现的，用于由薄隧道势垒形成的弱链接的情况：通过Josephson电流-相位关系，I = I(c)sin phi，其中I-c是取决于弱链接性质的临界电流，超电流I与相位差phi有关。类似的关系适用于由普通金属，半导体或收缩物组成的弱链接(2)。在所有情况下，当没有超电流流过结时，相位差为零，并且随着超电流的增加而单调增加，直到达到临界电流。在这里，我们使用纳米光刻技术制造了一个带有普通金属弱链接的约瑟夫森结，我们可以直接访问链接内部的微观载流电子状态。我们发现，通过控制正常金属中载流态的能量分布，基本约瑟夫森关系可以从I = I(c)sin变为I = I(c)sin(phi + pi)，即pi结。这些约瑟夫森结行为方式的根本改变，对它们在超导电子学以及基于超导体的（量子）逻辑电路中的应用具有潜在的影响。
When two superconductors are connected by a weak link, a supercurrent hows, the magnitude of which is determined by the difference in the macroscopic quantum phases of the superconductors. This phenomenon was discovered by Josephson(1) for the case of a weak link formed by a thin tunnel barrier: the supercurrent, I, is related to the phase difference, phi, through the Josephson current-phase relation, I = I(c)sin phi with I-c being the critical current which depends on the properties of the weak link A similar relation holds for weak links consisting of a normal metal, a semiconductor or a constriction(2). In all cases, the phase difference is zero when no supercurrent flows through the junction, and increases monotonically with increasing supercurrent until the critical current is reached. Here we use nanolithography techniques to fabricate a Josephson junction with a normal-metal weak link in which we have direct access to the microscopic current-carrying electronic states inside the link. We find that the fundamental Josephson relation can be changed from I = I(c)sin phi to I = I(c)sin(phi + pi)-that is, a pi-junction-by controlling the energy distribution of the current-carrying states in the normal metal. This fundamental change in the way these Josephson junctions behave has potential implications for their use in superconducting electronics as well as in (quantum) logic circuits based on superconductors.