Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea and Department of Physics, Chonbuk National University, Jeonju 561-756, Republic of Korea.
Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea and Department of Physics, Korea University, Seoul 136-713, Republic of Korea.
Phys Rev Lett. 2013 Feb 15;110(7):076803. doi: 10.1103/PhysRevLett.110.076803. Epub 2013 Feb 13.
We report nonequilibrium transport measurements of gate-tunable Andreev bound states in a carbon nanotube quantum dot coupled to two superconducting leads. In particular, we observe clear features of two types of Kondo ridges, which can be understood in terms of the interplay between the Kondo effect and superconductivity. In the first type (type I), the coupling is strong and the Kondo effect is dominant. Levels of the Andreev bound states display anticrossing in the middle of the ridge. On the other hand, crossing of the two Andreev bound states is shown in the second type (type II) together with the 0-π transition of the Josephson junction. Our scenario is well understood in terms of only a single dimensionless parameter, k(B)T(K)(min)/Δ, where T(K)(min) and Δ are the minimum Kondo temperature of a ridge and the superconducting order parameter, respectively. Our observation is consistent with measurements of the critical current, and is supported by numerical renormalization group calculations.
我们报告了在与两个超导引线耦合的碳纳米管量子点中进行的非平衡输运测量，这些测量涉及栅极可调的安德烈夫束缚态。特别是，我们观察到了两种类型的康多（Kondo）脊的明显特征，这些特征可以用康多效应和超导性之间的相互作用来理解。在第一种类型（I 型）中，耦合较强，康多效应占主导地位。安德烈夫束缚态的能级在脊的中间显示出反交叉。另一方面，在第二种类型（II 型）中，两个安德烈夫束缚态的交叉与约瑟夫森结的 0-π 跃迁一起出现。我们的方案仅用一个无量纲参数 k(B)T(K)(min)/Δ 就可以很好地理解，其中 T(K)(min)和 Δ 分别是脊的最小康多温度和超导有序参数。我们的观察结果与临界电流的测量结果一致，并得到数值重整化群计算的支持。
