Manipulation of the Kondo Effect via Two-Dimensional Molecular Assembly

Abstract

We report manipulation of a Kondo resonance originated from the spin-electron interactions between a twodimensional molecular assembly of TBrPP-Co molecules and a Cu(111) surface at 4.6 K using a low temperature scanning tunneling microscope. By manipulating nearest-neighbor molecules with a scanning tunneling microscope tip we are able to tune the spin-electron coupling of the center molecule inside a small hexagonal molecular assembly in a controlled step-by-step manner. The Kondo temperature increases from 105 to 170 K with a decreasing the number of nearest neighbor molecules from six to zero. This Kondo temperature variation is originated from the scattering of surface electrons by the molecules located at the edges of the molecular layer, which reduces spinelectron coupling strength for the molecules inside the layer. Investigations on different molecular arrangements indicate that the observed Kondo resonance is independent on the molecular lattice.

Spin coupling and relaxation inside molecule–metal contacts

“…Previous studies have shown that the Kondo temperature of metal-organic complexes can be manipulated by locally modifying the ligand field acting on the transition-metal ions 3,38 or by screening the surface electron density around molecular adsorbates by other molecules 39 .…”

Kondo effect in transport through molecules adsorbed on metal surfaces: From Fano dips to Kondo peaks

“…More recently [9] the Kondo temperature in a TBrPP-Co molecule adsorbed on a Cu(111) surface has been increased by decreasing the number of nearestneighbor TBrPP-Co molecules. The authors of [9] argued that this is due to a reduction of surfaces states when the number of nearest neighbors molecules around a given one is increased.One of the most interesting aspects of those two works is that while in the case of CoPc/Au(111) a Kondo peak was observed, in the experiments on TBrPP-Co/Cu(111) the conductance showed a Fano dip, as in isolated Co atoms adsorbed on metal surfaces [1,4,5]. Those two molecules, although largely different, have two outstanding similarities: i) both have the Co atom in the their geometric centers, and, ii) their STM images show four clearly defined lobes [6].…”

“…In particular it has been shown that, the characteristics, and even the existence, of the Kondo resonance can be controlled by distorting a CoPc molecule adsorbed on a Au(111) surface [6]. More recently [9] the Kondo temperature in a TBrPP-Co molecule adsorbed on a Cu(111) surface has been increased by decreasing the number of nearestneighbor TBrPP-Co molecules. The authors of [9] argued that this is due to a reduction of surfaces states when the number of nearest neighbors molecules around a given one is increased.…”

“…The possibility of tuning the Kondo temperature [6,9] has been recently demonstrated, increasing considerably the interest of these systems. In particular it has been shown that, the characteristics, and even the existence, of the Kondo resonance can be controlled by distorting a CoPc molecule adsorbed on a Au(111) surface [6].…”

“…Other model parameters have been varied aiming to identify their role in the behavior of this system, but always over ranges such that the main features in the conductance occur in energy scales similar to the experimental ones [9]. It is worth mentioning that in the present work U was taken always smaller than 3 eV, while in [8] a value of 8 eV was assumed.…”