Exchange Interaction between Single Magnetic Adatoms

Abstract

The magnetic coupling between single Co atoms adsorbed on a copper surface is determined by probing the Kondo resonance using low-temperature scanning tunneling spectroscopy. The Kondo resonance, which is due to magnetic correlation effects between the spin of a magnetic adatom and the conduction electrons of the substrate, is modified in a characteristic way by the coupling of the neighboring adatom spins. Increasing the interatomic distance of a Cobalt dimer from 2.56 to 8.1 A we follow the oscillatory transition from ferromagnetic to antiferromagnetic coupling. Adding a third atom to the antiferromagnetically coupled dimer results in the formation of a collective correlated state.

Nonequilibrium spin-current detection with a single Kondo impurity

“…It is now possible to tackle nontrivial many-body effects in a controlled environment. 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.…”

A non-perturbative treatment of quantum impurity problems in real lattices

“…More recently, the dispersion of surface states has also been studied in Cu and Ag using an STM [150]. First principles and analytic calculations have predicted long-ranged oscillatory adsorbate-adsorbate interactions mediated by these surface states [48,151,152]. Their findings are consistent with a 2D RKKY interaction that decays asymptotically as ∼ 1/R 2 .…”

“…Another popular subject of research is the behavior of magnetic adatoms on the surface of noble metals, whose (111) surface is known to host a surface state [46][47][48]. The competition between temperature, magnetic field, and Kondo, of organic molecules on gold has also been studied by STM methods [14].…”

“…[133][134][135] This technique can, for example, uncover spatial profiles of magnetic excitations in artificial one-dimensional spin chains [136][137][138][139]. The surface not only supports the spin centres, but also plays a crucial role in stabilizing magnetic order [48,[140][141][142]. The impurities are coupled through exchange interactions of different physical origins, either direct exchange for nearest-neighbor adsorption sites or indirect substrate-mediated coupling that asymptotically decay as a power-law with increasing separation between the impurities (RKKY interaction) [8][9][10].…”

Transport properties of a two-impurity system: A theoretical approach

“…The parameter that drives the system through the phase diagram is the ratio I/T 0 K , where I is the inter-impurity exchange interaction and T 0 K is the Kondo temperature of the individual impurities (assumed to be identical). This system has received great attention both theoretically (see below) and experimentally [2][3][4][5][6] . Experiments performed in two-impurity systems have been able to carry it from the Kondo screened phase to the antiferromagnetic (AF) regime, but without achieving a precise control of the exchange interaction between the two impurities.…”