The role of magnetic anisotropy in the Kondo effect

Abstract

In the Kondo effect, a localized magnetic moment is screened by forming a correlated electron system with the surrounding conduction electrons of a non-magnetic host 1 . Spin S = 1/2 Kondo systems have been investigated extensively in theory and experiments, but magnetic atoms often have a larger spin 2 . Larger spins are subject to the influence of magnetocrystalline anisotropy, which describes the dependence of the magnetic moment's energy on the orientation of the spin relative to its surrounding atomic environment 3,4 . Here we demonstrate the decisive role of magnetic anisotropy in the physics of Kondo screening. A scanning tunnelling microscope is used to simultaneously determine the magnitude of the spin, the magnetic anisotropy and the Kondo properties of individual magnetic atoms on a surface. We find that a Kondo resonance emerges for large-spin atoms only when the magnetic anisotropy creates degenerate ground-state levels that are connected by the spin flip of a screening electron. The magnetic anisotropy also determines how the Kondo resonance evolves in a magnetic field: the resonance peak splits at rates that are strongly direction dependent. These rates are well described by the energies of the underlying unscreened spin states.A low density of magnetic impurities in a non-magnetic host metal can have dramatic effects on the magnetic, thermodynamic and electrical properties of the material owing to the Kondo effect, a many-body interaction between the metal's conduction electrons and the electron spin of the localized magnetic impurity 5 . This interaction gives rise to a narrow, pronounced peak in the density of states close to the Fermi energy 1 . The past decade has seen a surge of interest in the Kondo screening of individual atomic spins, as a result of experimental advances in probing individual magnetic atoms by using scanning tunnelling microscopes 6,7 and single-molecule transistors 8,9 . When magnetic atoms are placed on metal surfaces the Kondo interaction between the localized spin and the conduction electrons is very strong, leading to high Kondo temperatures T K , in the range from 40 to 200 K (ref. 10). In order to probe the Kondo physics it is desirable to reduce this interaction so that the Kondo screening competes on an equal footing with external influences such as magnetic fields. It was shown recently that this can be achieved by incorporating a decoupling layer between the atomic spin and the screening conduction electrons 11 .

Entanglement perturbation theory for the elementary excitation in one dimension

“…While the applications of EPT-e to 1D fermions and bosons are straightforward, we need yet to see how it works in two dimensions. Finally, the successful calculation of the excitation spectrum indicates that EPT can handle various nanostructures embedded in correlated host materials, opening a possible new look at the Kondo effect [21].…”

Electron Transport in Magnetic Quantum Point Contacts

“…In this respect, an interesting question concerns the role of magnetism and the effect of the electron spin on the transport properties of such a contact. Since this issue is also technologically important, especially in the view of novel concepts for data storage [14][15][16][17], the study of transport through individual magnetic atoms and molecules has become the subject of intensive studies [15,[18][19][20][21][22]. Despite the immense progress in the field there are numerous open questions, e.g.…”

Optically and Electrically Controllable Adatom Spin–orbital Dynamics in Transition Metal Dichalcogenides

“…Our ab initio calculations suggest that d 9 configurations are realizable by single Co, Rh, or Ir adatoms on MoS2, which additionally exhibit a sizable magnetic anisotropy. We find that the interaction of the adatom with carriers in the MX2 allows to tune its behavior from a quantum regime with full Kondo screening to a regime of "Ising spintronics" where its spin-orbital moment acts as classical bit, which can be erased and written electronically and optically.Transition metal adatoms on surfaces provide ideal model systems for fundamental studies of quantum many-body phenomena ranging from magnetism [1][2][3] and Kondo physics [4][5][6][7] to topological states of matter [8][9][10] and Majorana modes [11][12][13]. Moreover, these systems are promising as ultimately miniaturized building blocks of spintronic devices and logic gates.…”