0-$\pi$ quantum transition in a carbon nanotube Josephson junction: universal phase dependence and orbital degeneracy

Abstract

We investigate experimentally the supercurrent in a clean carbon nanotube quantum dot, close to orbital degeneracy, connected to superconducting leads in a regime of strong competition between local electronic correlations and superconducting proximity effect. For an odd occupancy of the dot and intermediate coupling to the reservoir, the Kondo effect can develop in the normal state and screen the local magnetic moment of the dot. This leads to singlet-doublet transitions that strongly affect the Josephson effect in a single-level quantum dot: the sign of the supercurrent changes from positive to negative (0 to $\pi$-junction). In the regime of strongest competition between the Kondo effect and proximity effect, meaning that the Kondo temperature equals the superconducting gap, the magnetic state of the dot undergoes a first order quantum transition induced by the superconducting phase difference across the junction. This is revealed experimentally by anharmonic current-phase relations. In addition, the very specific electronic configuration of clean carbon nanotubes, with two nearly orbitally degenerated states, leads to different physics depending whether only one or both quasi-degenerate upper levels of the dots participate to transport, which is determined by their occupancy and relative widths. When the transport of Cooper pairs takes place through only one of these levels, we find that the phase diagram of the phase-dependent 0-$\pi$ transition is a universal characteristic of a discontinuous level-crossing quantum transition at zero temperature. In the case were two levels participate to transport, the nanotube Josephson current exhibits a continuous 0-$\pi$ transition, independent of the superconducting phase, revealing a different physical mechanism of the transition.

14 pages, 12 figures

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• Josephson ${\phi }_0$-junction in nanowire quantum dots
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• Josephson current through a single Anderson impurity coupled to BCS leads
• Even-odd effect in Andreev Transport through a Carbon Nanotube Quantum Dot
• Kondo-Enhanced Andreev Tunneling in InAs Nanowire Quantum Dots
• SU(4) and SU(2) Kondo Effects in Carbon Nanotube Quantum Dots
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• Transport Measurement of Andreev Bound States in a Kondo-Correlated Quantum Dot
• Manipulating the magnetic state of a carbon nanotube Josephson junction using the superconducting phase
• Josephson current through interacting double quantum dots with spin-orbit coupling

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• Two-Impurity Yu-Shiba-Rusinov States in Coupled Quantum Dots
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• Inductive microwave response of Yu-Shiba-Rusinov states
• Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions
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• Correlation effects in superconducting quantum dot systems
• Phase-Coherent Dynamics of Quantum Devices With Local Interactions
• Field-free Josephson diode effect in interacting chiral quantum dot junctions
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• The carbon nanotube gatemon qubit
• Unified theory of quantum phase transitions in quantum dots with gapped host bands
• Noise of a chargeless Fermi liquid
• Ballistic SNS sandwich as a Josephson junction
• Andreev spin-noise detector
• Collapse of the Josephson emission in a carbon nanotube junction in the Kondo regime
• Josephson junctions based on ultraclean carbon nanotubes
• Supercurrent from the imaginary part of the Andreev levels in non-Hermitian Josephson junctions
• Mixed-Valence Transition on a Quantum-Dot Coupled to Superconducting and Spin-Polarized Leads
• Radio-frequency characterization of a supercurrent transistor made from a carbon nanotube
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• Probing the topological protection of edge states in multilayer tungsten ditelluride with the superconducting proximity effect
• Slave-spin approach to the Anderson-Josephson quantum dot