Reversible switching of Kondo resonance in a single-molecule junction

The control of the Kondo effect is of great interest in single-molecule junction due to its potential applications in spin based electronics.Here,we demonstrate that the Kondo effect is reversibly switched on and off in an iron phthalocyanine(FePc)single-molecule junction by using a superconducting Nb tip.In a scanning tunneling microscope-based Nb-insulator-FePc-Au junction,we achieve a reversible switching between the Kondo dip and inelastic electronic tunneling spectra by simply adjusting the tip-sample distance to tune the tunnel coupling at low temperature.Further approaching the tip leads to the picking up of the molecule to the tip apex,which transfers the geometry of the single-molecule junction into a Nb-FePc-insulator-Au type.As the molecule forms an effective magnetic impurity embedded into the superconducting ground states of the Nb tip,the out-gap Kondo dip switched to an in-gap Yu-Shiba-Rusinov state.Our results open up a new route for manipulating the Kondo effect within a single-molecule junction.

Kondo resonance assisted thermoelectric transport through strongly correlated quantum dots

We theoretically studied the thermoelectric transport properties of a strongly correlated quantum dot system in the presence of the Kondo effect based on accurate numerical evaluations using the hierarchical equations of motion approach.The thermocurrent versus gate voltage shows a distinct sawtooth line-shape at high temperatures.In particular,the current changes from positive(hole charge)to negative(particle charge)in the electron number N=1 region due to the Coulomb blockade effect.However,at low temperatures,where the Kondo effect occurs,the thermocurrent’s charge polarity reverses,along with a significantly enhanced magnitude.As anticipated,the current sign can be analyzed by the occupation difference between particle and hole.Moreover,the characteristic turnover temperature can be further defined at which the influences of the Coulomb blockade and Kondo resonance are in an effective balance.Remarkably,the identified characteristic turnover temperature,as a function of the Coulomb interaction and dot-lead coupling,possessed a much higher value than the Kondo temperature.When a magnetic field is applied,a spin-polarized thermocurrent can be obtained,which could be tested in future experiments.

Fano Resonance in Landau Fermi and Luttinger Liquids

With a two-channel model, we study the influence of temperature, external voltage and magnetic flux on the line shape of the Fano resonance, and show that in the Luttinger liquid case, the background transmittance and the asymmetric parameter depend strongly on the temperature and external voltage, while for the Landau Fermi liquid case they are nearly independent of these parameters in the low energy region. Moreover, we demonstrate that the asymmetric parameter changes periodically with an external magnetic flux, which is consistent with the recent experimental data.

Uncovering the magnetic response of open-shell graphene nanostructures on metallic surfaces at different doping levels

Open-shell graphene nanostructures(GNs)are promising candidates for future spintronics and quantum technologies.Recent progress based on on-surface synthetic approach has successfully created such GNs on metallic surfaces.Meanwhile,the doping effect of metallic surfaces is inevitably present and can significantly tune their electronic and magnetic properties.Here,we investigate the zigzag end states of open-shell 7-armchair graphene nanoribbons(7-AGNRs)on Au(111),Au(100)and Ag(111)surfaces.Combined with the manipulation of a scanning tunneling microscope,we demonstrate that the end states can be tuned from empty states to singly occupied states and to doubly occupied states by substrate doping.Furthermore,the singly occupied states can be finely tuned,with the occupancy number of the states and related magnetic behaviors uncovered by experiments at different temperatures and magnetic fields.Our results provide a comprehensive study of the magnetic response of open-shell GNs on metallic surfaces at different doping levels.

Two-impurity Kondo effect in potassium-doped single-layer p-sexiphenyl films

Herein, we show that a self-assembled phase of potassium(K)-doped single-layer para-sexiphenyl(PSP) film on a gold substrate is an excellent platform for studying the two-impurity Kondo model. On K-doped PSP molecules well separated from others, we observe a Kondo resonance peak close to EFwith a Kondo temperature of 30 K. The Kondo resonance peak splits when another K-doped PSP molecule is present in the vicinity, and the splitting gradually increases with the decrease in intermolecular distance without signs of phase transition. Our data demonstrate how a Kondo singlet state gradually evolves into an antiferromagnetic singlet state due to the competition between Kondo screening and antiferromagnetic Ruderman-Kittel-Kasuya-Yosida coupling,as described in the two-impurity Kondo model. Intriguingly, the antiferromagnetic singlet is quickly destroyed on increasing temperature and transforms back to a Kondo singlet below the Kondo temperature. Our data provide a comprehensive picture and quantitative constraints on related theories and calculations of the two-impurity Kondo model.