Subgap resonant quasiparticle transport in normal-superconductor quantum dot devices

Abstract

We report thermally activated transport resonances for biases below the superconducting energy gap in a carbon nanotube (CNT) quantum dot (QD) device with a superconducting Pb and a normal metal contact. These resonances are due to the superconductor's finite quasi-particle population at elevated temperatures and can only be observed when the QD life-time broadening is considerably smaller than the gap. This condition is fulfilled in our QD devices with optimized Pd/Pb/In multi-layer contacts, which result in reproducibly large and "clean" superconducting transport gaps with a strong conductance suppression for subgap biases. We show that these gaps close monotonically with increasing magnetic field and temperature. The accurate description of the subgap resonances by a simple resonant tunneling model illustrates the ideal characteristics of the reported Pb contacts and gives an alternative access to the tunnel coupling strengths in a QD.

6 pages, 3 figures

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Cited by in corpus (15)

• Epitaxial Pb on InAs nanowires
• Andreev bound states probed in three-terminal quantum dots
• Spectroscopy of the superconducting proximity effect in nanowires using integrated quantum dots
• Majorana quasiparticles in semiconducting carbon nanotubes
• Large spatial extension of the zero-energy Yu-Shiba-Rusinov state in magnetic field
• From Cooper pair splitting to the non-local spectroscopy of a Shiba state
• Superconducting contacts to a monolayer semiconductor
• Current cross-correlations in double quantum dot based Cooper pair splitters with ferromagnetic leads
• Nonlocal measurement of quasiparticle charge and energy relaxation in proximitized semiconductor nanowires using quantum dots
• Charge-vibration interaction effects in normal-superconductor quantum dots
• Spin-resolved spectroscopy using a quantum dot defined in InAs 2DEG
• Spin-filtered measurements of Andreev bound states
• Effective Long-Range Pairing and Hopping in Topological Nanowires Weakly Coupled to $s$-Wave Superconductors
• Non-equilibrium properties of graphene probed by superconducting tunnel spectroscopy
• A particle conserving approach to AC-DC driven interacting quantum dots with superconducting leads