Tuning the Kondo Effect with a Mechanically Controllable Break Junction

Parks, J. J.; Champagne, A. R.; Hutchison, Geoffrey; Flores-Torres, Samuel; Abruña, Héctor D.; Ralph, Daniel

doi:10.1103/physrevlett.99.026601

Cited by 192 publications

(241 citation statements)

References 35 publications

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“…Several arguments are in favor of this situation: i) tunneling from the electrodes is typically monomode because the electromigration process is stopped at the breaking up of the metallic contacts; ii) coupling of the molecule to the source and drain is also typically quite asymmetric (conductance maxima of Kondo anomalies in molecules range from a few per-thousands to half the conductance quantum [13]); iii) the two molecular orbitals involved can also be asymmetrically coupled to the leads, as is seen at least in our device, see discussion in section 2.2.…”

Section: Triplet Side: Spin S = 1 Underscreened Kondo Effectmentioning

confidence: 99%

Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund’s rule, underscreened Kondo effect and quantum phase transitions

Florens

Freyn

Roch

et al. 2011

J. Phys.: Condens. Matter

110

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Abstract. We review here some universal aspects of the physics of two-electron molecular transistors in the absence of strong spin-orbit effects. Several recent quantum dots experiments have shown that an electrostatic backgate could be used to control the energy dispersion of magnetic levels. We discuss how the generically asymmetric coupling of the metallic contacts to two different molecular orbitals can indeed lead to a gate-tunable Hund's rule in the presence of singlet and triplet states in the quantum dot. For gate voltages such that the singlet constitutes the (non-magnetic) ground state, one generally observes a suppression of low voltage transport, which can yet be restored in the form of enhanced cotunneling features at finite bias. More interestingly, when the gate voltage is controlled to obtain the triplet configuration, spin S = 1 Kondo anomalies appear at zero-bias, with non-Fermi liquid features related to the underscreening of a spin larger than 1/2. Finally, the small bare singlet-triplet splitting in our device allows to fine-tune with the gate between these two magnetic configurations, leading to an unscreening quantum phase transition. This transition occurs between the non-magnetic singlet phase, where a two-stage Kondo effect occurs, and the triplet phase, where the partially compensated (underscreened) moment is akin to a magnetically "ordered" state. These observations are put theoretically into a consistent global picture by using new Numerical Renormalization Group simulations, taylored to capture sharp finie-voltage cotunneling features within the Coulomb diamonds, together with complementary outof-equilibrium diagrammatic calculations on the two-orbital Anderson model. This work should shed further light on the complicated puzzle still raised by multi-orbital extensions of the classic Kondo problem.

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Section: Triplet Side: Spin S = 1 Underscreened Kondo Effectmentioning

confidence: 99%

Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund’s rule, underscreened Kondo effect and quantum phase transitions

Florens

Freyn

Roch

et al. 2011

J. Phys.: Condens. Matter

110

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“…The signature of nuclear motion has been observed in conduction measurements of a variety of molecular junctions, 11,14,16,18,19,[25][26][27][35][36][37][38][39][40][41][42][43][44][45][46] e.g., H 2 between platinum electrodes, 14 C 60 molecules between gold electrodes, 11 and copper phthalocyanine 19 on aluminum oxide film. Vibrational signatures of molecular bridges have also been observed in inelastic electron tunneling spectroscopy.…”

Section: Introductionmentioning

confidence: 96%

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

Wang

Pshenichnyuk

Härtle

et al. 2011

The Journal of Chemical Physics

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The multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory within second quantization representation of the Fock space, a novel numerically exact methodology to treat manybody quantum dynamics for systems containing identical particles, is applied to study the effect of vibrational motion on electron transport in a generic model for single-molecule junctions. The results demonstrate the importance of electronic-vibrational coupling for the transport characteristics. For situations where the energy of the bridge state is located close to the Fermi energy, the simulations show the time-dependent formation of a polaron state that results in a pronounced suppression of the current corresponding to the phenomenon of phonon blockade. We show that this phenomenon cannot be explained solely by the polaron shift of the energy but requires methods that incorporate the dynamical effect of the vibrations on the transport. The accurate results obtained with the ML-MCTDH in this parameter regime are compared to results of nonequilibrium Green's function theory.

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“…Interestingly, several theoretical works predict a more exotic Kondo arising from the magnetic anisotropy and high spin of SMM; i.e., high-spin under-screened Kondo and quantum-spin tunneling Kondo 33 . Under-screened Kondo has been observed in a C 60 molecule 34,35 , but its experimental observation in SMM with larger spin still remains an open challenge to the best of our knowledge.…”

Section: Kondo Effectmentioning

confidence: 99%

Observing magnetic anisotropy in electronic transport through individual single-molecule magnets

Burzurí

Gaudenzi²,

Zant³

2015

J. Phys.: Condens. Matter

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We review different electron transport methods to probe the magnetic properties, such as the magnetic anisotropy, of an individual Fe4 SMM. The different approaches comprise first and higher order transport through the molecule. Gate spectroscopy, focusing on the charge degeneracy-point, is presented as a robust technique to quantify the longitudinal magnetic anisotropy of the SMM in different redox states. We provide statistics showing the robustness and reproducibility of the different methods. In addition, conductance measurements typically show high-energy excited states well beyond the ground spin multiplet of SMM. Some of these excitations have their origin in excited spin multiplets, others in vibrational modes of the molecule. The interplay between vibrations, charge and spin may yield a new approach for spin control.

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Tuning the Kondo Effect with a Mechanically Controllable Break Junction

Cited by 192 publications

References 35 publications

Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund’s rule, underscreened Kondo effect and quantum phase transitions

Universal transport signatures in two-electron molecular quantum dots: gate-tunable Hund’s rule, underscreened Kondo effect and quantum phase transitions

Numerically exact, time-dependent treatment of vibrationally coupled electron transport in single-molecule junctions

Observing magnetic anisotropy in electronic transport through individual single-molecule magnets

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