Finite-bias conductance anomalies at a singlet-triplet crossing

Abstract

Quantum dots and single-molecule transistors may exhibit level crossings induced by tuning external parameters such as magnetic field or gate voltage. For Coulomb blockaded devices, this shows up as an inelastic cotunneling threshold in the differential conductance, which can be tuned to zero at the crossing. Here we show that, in addition, level crossings can give rise to a nearly vertical step-edge, ridge or even a Fano-like ridge-valley feature in the differential conductance inside the relevant Coulomb diamond. We study a gate-tunable quasidegeneracy between singlet and triplet ground states, and demonstrate how these different shapes may result from a competition between nonequilibrium occupations and weak (spin-orbit) mixing of the states. Our results are shown to be in qualitative agreement with recent transport measurements on a Mn complex [E. A. Osorio, et al., Nano Lett. 10, 105 (2010)]. The effect remains entirely general and should be observable in a wide range of Coulomb blockaded devices.

arXiv comment8 pages, 6 figures. Published version

References in corpus (17)

• Kondo physics in carbon nanotubes
• Quantum phase transition in a single-molecule quantum dot
• Direct Measurement of the Spin-Orbit Interaction in a Two-Electron InAs Nanowire Quantum Dot
• Electron Cotunneling in a Semiconductor Quantum Dot
• Zero-bias anomalies and boson-assisted tunneling through quantum dots
• Electric-field controlled spin reversal in a quantum dot with ferromagnetic contacts
• Kinetic Equations for Transport Through Single-Molecule Transistors
• Electrical manipulation of spin states in a single electrostatically gated transition-metal complex
• Hybrid superconductor-semiconductor devices made from self-assembled SiGe nanocrystals on silicon
• Nonequilibrium Singlet-Triplet Kondo Effect in Carbon Nanotubes
• Singlet-triplet transition in a single-electron transistor at zero magnetic field
• Density-operator approaches to transport through interacting quantum dots: Simplifications in fourth-order perturbation theory
• Kondo effect induced by a magnetic field
• Pair tunneling through single molecules
• Cotunneling-mediated transport through excited states in the Coulomb blockade regime
• Pair-tunneling resonance in the single-electron transport regime
• Dzyaloshinskii-Moriya interaction in transport through single molecule transistors

Cited by in corpus (5)

• Ground-state spin blockade in a single-molecule junction
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• Transport mirages in single-molecule devices
• Charge fluctuations in nonlinear heat transport
• Magnetically-Tuned Kondo Effect in a Molecular Double Quantum Dot: Role of the Anisotropic Exchange