2006/08/01 by Jorden A. van Dam, Yuli V. Nazarov, Erik P. A. M. Bakkers +3 · 4 citations
Physics and Astronomy · #Charge (physics) #Condensed matter physics #Electron #Josephson effect #Physics #Physics of Superconductivity and Magnetism #Pi Josephson junction #Quantum and electron transport phenomena #Quantum dot #Quantum mechanics #Quantum point contact #Quantum tunnelling #Quantum well #Semiconductor Quantum Structures and Devices #Superconducting tunnel junction #Superconductivity #Supercurrent #cond-mat.mes-hall #cond-mat.supr-con
paper · pdf · doi:10.1038/nature05018
published as Nature 442, 667-670 (2006)
openalex publication_date 2006/08/01 · arxiv created 2006/09/28 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
When two superconductors become electrically connected by a weak link a zero-resistance supercurrent can flow. This supercurrent is carried by Cooper pairs of electrons with a combined charge of twice the elementary charge, e. The 2e charge quantum is clearly visible in the height of Shapiro steps in Josephson junctions under microwave irradiation and in the magnetic flux periodicity of h/2e in superconducting quantum interference devices. Several different materials have been used to weakly couple superconductors, such as tunnel barriers, normal metals, or semiconductors. Here, we study supercurrents through a quantum dot created in a semiconductor nanowire by local electrostatic gating. Due to strong Coulomb interaction, electrons only tunnel one-by-one through the discrete energy levels of the quantum dot. This nevertheless can yield a supercurrent when subsequent tunnel events are coherent. These quantum coherent tunnelling processes can result in either a positive or a negative supercurrent, i.e. in a normal or a pi-junction, respectively. We demonstrate that the supercurrent reverses sign by adding a single electron spin to the quantum dot. When excited states of the quantum dot are involved in transport, the supercurrent sign also depends on the character of the orbital wavefunctions.