Tunneling into a Single Magnetic Atom: Spectroscopic Evidence of the Kondo Resonance

Abstract

The Kondo effect arises from the quantum mechanical interplay between the electrons of a host metal and a magnetic impurity and is predicted to result in local charge and spin variations around the magnetic impurity. A cryogenic scanning tunneling microscope was used to spatially resolve the electronic properties of individual magnetic atoms displaying the Kondo effect. Spectroscopic measurements performed on individual cobalt atoms on the surface of gold show an energetically narrow feature that is identified as the Kondo resonance-the predicted response of a Kondo impurity. Unexpected structure in the Kondo resonance is shown to arise from quantum mechanical interference between the d orbital and conduction electron channels for an electron tunneling into a magnetic atom in a metallic host.

Single-molecule transistors: Electron transfer in the solid state

“…Investigations of individual Co atoms on Au(1 1 1) surfaces [5,45] have found a Kondo temperature for that system of $70 K. A detailed electronic structure study of charge transfer between the Co atom and the Au(1 1 1) surface combined with sophisticated manybody calculations of the Kondo correlations has successfully understood this result [46].…”

“…Assuming that the electronic density of states of the tip is relatively featureless, this technique, known as scanning tunneling spectroscopy (STS), allows the measurement of the local density of states induced by the molecule. This novel spectroscopy has been revelatory, allowing the solid state observation of the alignment and broadening of occupied molecular orbitals [1], vibronic effects [2], inelastic electron tunneling via molecular vibrations [3] and spin flips [4], and electronic correlations such as Kondo physics [5].…”

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.…”

Observing Spin Polarization of Individual Magnetic Adatoms

“…Additionally, Spin-coupling of conduction electrons to single magnetic atoms has been observed via the Kondo effect (8,9), and spin-flips have been observed via inelastic tunneling through individual magnetic atoms (10,11) and magnetic resonance force microscopy of silicon defects (12). Direct observation of the spin-polarization state of isolated adatoms, however, remains challenging, in part because isolated atoms have low magnetic anisotropy energy (MAE) which causes their spin to fluctuate in time due to environmental interactions.…”