Aharonov-Bohm环内量子点约瑟夫森结的超导和多重单重态-二重态相变
Supercurrent and multiple singlet-doublet phase transitions of a quantum dot Josephson junction inside an Aharonov-Bohm ring
摘要：
我们研究了Aharonov-Bohm环境中的量子点约瑟夫森结。的几何形状是由安德森杂质耦合到两个直接连接的BCS引线。我们说明，由两个不同的（单重态和双重态）相位的相互作用所支配的低能量物理学的公认的图片仍然是有效的这种干涉设置。然而，相边界非单调地依赖于超导体之间的耦合强度，导致系统表现出重入行为和多个相变。我们计算了零温约瑟夫森电流，并证明了它可以成为负的单重态凭借库仑相互作用U。作为出发点，解析求解了大超导能隙极限Δ= \infty。为了处理任意的Δ < \infty and U>0，我们采用了截断泛函重整化群方案，这是以前证明给定量可靠的结果的量子点约瑟夫森问题。
英文摘要：
We study a quantum dot Josephson junction inside an Aharonov-Bohm environment. The geometry is modeled by an Anderson impurity coupled to two directly-linked BCS leads. We illustrate that the well-established picture of the low-energy physics being governed by an interplay of two distinct (singlet and doublet) phases is still valid for this interferometric setup. The phase boundary depends, however, non-monotonically on the coupling strength between the superconductors, causing the system to exhibit re-entrance behavior and multiple phase transitions. We compute the zero-temperature Josephson current and demonstrate that it can become negative in the singlet phase by virtue of the Coulomb interaction U. As a starting point, the limit of large superconducting energy gaps Δ=\infty is solved analytically. In order to tackle arbitrary Δ<\infty and U>0, we employ a truncated functional renormalization group scheme which was previously demonstrated to give quantitatively reliable results for the quantum dot Josephson problem.
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