Magnetically Tuned Kondo Effect in a Molecular Double Quantum Dot
Role of the Anisotropic Exchange
Peter Zalom (Univerzita Karlova, Czech Academy of Sciences)
Joeri De Bruijckere (TU Delft - Applied Sciences, Kavli institute of nanoscience Delft)
Rocco Gaudenzi (Kavli institute of nanoscience Delft, Max Planck Institute for the History of Science, Berlin)
Herre S.J. Van Der Zant (TU Delft - Applied Sciences, Kavli institute of nanoscience Delft)
Tomáš Novotný (Univerzita Karlova)
Richard Korytár (Univerzita Karlova)
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Abstract
We investigate theoretically and experimentally the singlet-triplet Kondo effect induced by a magnetic field in a molecular junction. Temperature-dependent conductance, G(T), is calculated by the numerical renormalization group, showing a strong imprint of the relevant low-energy scales, such as the Kondo temperature, exchange, and singlet-triplet splitting. We demonstrate the stability of the singlet-triplet Kondo effect against weak spin anisotropy, modeled by an anisotropic exchange. Moderate spin anisotropy manifests itself by lowering the Kondo plateaus, causing the G(T) to deviate from a standard temperature dependence, expected for a spin-half Kondo effect. We propose this scenario as an explanation for anomalous G(T), measured in an organic diradical molecule coupled to gold contacts. We uncover certain new aspects of the singlet-triplet Kondo effect, such as coexistence of spin-polarization on the molecule with Kondo screening and nonperturbative parametric dependence of an effective magnetic field induced by the leads.