Symmetry-Driven Novel Kondo Effect in a Molecule

Abstract

The Kondo effect caused by the adsorption of iron phthalocyanine (FePc) on Au(111) was investigated by the combination of density functional theory and a numerical renormalization group calculation with scanning tunneling microscopy. We found that a novel Kondo effect is realized for a single FePc molecule on Au(111) by tuning the symmetry of the ligand field through the local coordination to the substrate. For FePc in the on top configuration where fourfold symmetry around the Fe(2+) ion is held, the orbital degrees of freedom survive, resulting in the spin+orbital SU(4) Kondo effect. In contrast, the reduced symmetry in the bridge configuration freezes the orbital degrees of freedom, leading to the spin SU(2) Kondo effect. These results provide a novel example to manipulate the many-body phenomena by tuning the local symmetry.

Nonequilibrium spin-current detection with a single Kondo impurity

“…The Kondo resonance has been investigated through scanning tunneling microscopy (STM) in single atoms either isolated [2][3][4] or coupled to other atoms, [5][6][7][8] in single-atom contacts, [9][10][11] and in single molecules. [12][13][14][15][16] It has also been successfully evidenced in nanoscale devices, [17][18][19][20][21] in particular quantum dots, [17][18][19][22][23][24] carbon nanotubes, [25][26][27] and nanowires. 28 Of particular interest-especially in the context of spintronics, is the issue of screening in the presence of a magnetic environment such as spin-polarized electrodes [29][30][31][32][33][34][35] and spinpolarized edge states.…”

Kondo behavior and conductance through 3d impurities in gold chains doped with oxygen

“…However often in practice the symmetry corresponds to a larger Lie group, the SU(4) one, leading to another exotic Kondo effect. In fact the low-energy effective Hamiltonian for a molecule of iron(II) phtalocyanine on Au(111) has SU(4) symmetry [12,26]. This is also the case for quantum dots in carbon nanotubes [27,28,29,30,31,32,33,34,35].…”

“…In all the listed cases we consider U = 0 at the impurity sites. [12]), the physics would be the same as that for a Co impurity (discussed below). In this case, we have also investigated the effect of U within GGA+U to gain more insight into the charge distribution.…”

“…Assuming integer occupancies one has an orbitally degenerate S = 2 impurity screened by three channels. One would expect a two-stage partial screening, first by the 5d 3z 2 −r 2 Au conduction states which have a larger hybridization, and then by the 5d xz and 5d yz , with some similarities to iron(II) phtalocyanine molecules on Au(111) [12], but here the ground state would have S = 1.…”

“…In the last years there has been a great amount of experiments in electronic transport through semiconducting [1,2,3,4,5,6,7] and molecular [8,9,10,11,12] quantum dots (QDs), in which manifestations of the Kondo effect were observed. In addition, experiments with mechanically controllable break junctions made possible to create one-dimensional atomic chains of several elements [13,14,15], and the conductance of noble-metal nanowires with transition-metals impurities has been measured using point-contact techniques [16,17].…”