title: Transport measurement of Andreev bound states in a Kondo-correlated quantum dot.
abstract: 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.
authors.affiliation: 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.
authors.forename: Bum-Kyu
authors.initials: BK
authors.lastname: Kim
authors.affiliation: 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.
authors.forename: Ye-Hwan
authors.initials: YH
authors.lastname: Ahn
authors.affiliation: Department of Physics, Chonbuk National University, Jeonju 561-756, Republic of Korea.
authors.forename: Ju-Jin
authors.initials: JJ
authors.lastname: Kim
authors.affiliation: Department of Physics, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Mahn-Soo
authors.initials: MS
authors.lastname: Choi
authors.affiliation: Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea.
authors.forename: Myung-Ho
authors.initials: MH
authors.lastname: Bae
authors.affiliation: Department of Physics, Chonnam National University, Gwangju 500-757, Republic of Korea.
authors.forename: Kicheon
authors.initials: K
authors.lastname: Kang
authors.affiliation: Institut de Física Interdisciplinar i de Sistemes Complexos IFISC (CSIC-UIB), E-07122 Palma de Mallorca, Spain.
authors.forename: Jong Soo
authors.initials: JS
authors.lastname: Lim
authors.affiliation: Institut de Física Interdisciplinar i de Sistemes Complexos IFISC (CSIC-UIB), E-07122 Palma de Mallorca, Spain and Departament de Física, Universitat de les Illes Balears, E-07122 Palma de Mallorca, Spain.
authors.forename: Rosa
authors.initials: R
authors.lastname: López
authors.affiliation: Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea.
authors.forename: Nam
authors.initials: N
authors.lastname: Kim