Theory Meets Experiment in Low-Dimensional Structures with Correlated Electrons
Prague, Czech Republic, July 1 – 4, 2019
Following the Kondo temperature of a tunable single-molecule junction continuously from the Kondo singlet to the free spin 1/2 ground state
We monitor the conductance evolution by varying the coupling between an organic molecule and the Ag(111) surface by lifting the molecule from the surface with the tip of a scanning tunneling microscope. Numerical renormalization group theory analysis of the junction conductance reveals that the system is tuned from the strongly coupled Kondo singlet to the free spin 1/2 ground state. In the crossover between the strong and weak coupling regimes, where the Kondo temperature TK is similar to the experimental Texp, fitting procedures generically provide ambiguous estimates of TK that tend to vary by an order of magnitude. Measuring the dependence of the junction conductance in external magnetic fields resolves this ambiguity if the Zeeman splitting due to the imposed magnetic field overcomes the thermal energy kBTexp. We demonstrate that Frota analysis overestimates TK by several orders of magnitude in the transient and weak coupling regimes. The numerical analysis also allows us to determine molecular coupling to surface and tip and their evolution during the lifting process.