Abstract:Due to underlying symmetries the ground states of magnetic adatoms may be
highly stable, which opens perspectives for application as single-atom memory.
A specific example is a single holmium atom (with $J=8$) on a platinum (111)
surface for which exceptionally long lifetimes were observed in recent scanning
tunneling microscopy studies. For control and read-out the atom must be coupled
to electronic contacts. Hence the spin dynamics of the system is governed by a
quantum master equation. Our analysis shows th… Show more
“…The transition from the initial magnetically polarized state to the final paramagnetic state in the quantum regime is a complex problem 24 and we leave the theoretical description of the magnetization dynamics for future considerations. Nonetheless, we notice that if we assume Δ ex = 0 while keeping all other parameters in Eq.…”
We address a recent controversy concerning the magnetic state of holmium adatom on platinum surface. Within a combination of the density functional theory (DFT) with the exact diagonalization (ED) of Anderson impurity model, the 〈J
z〉 = 0 paramagnetic ground state |J = 8, J
z = ±8〉 is found. In an external magnetic field, this state is transformed to a spin-polarized state with 〈J
z〉 ≈ 6.7. We emphasize the role of 5d–4f interorbital exchange polarization in modification of the 4f shell energy spectrum.
“…The transition from the initial magnetically polarized state to the final paramagnetic state in the quantum regime is a complex problem 24 and we leave the theoretical description of the magnetization dynamics for future considerations. Nonetheless, we notice that if we assume Δ ex = 0 while keeping all other parameters in Eq.…”
We address a recent controversy concerning the magnetic state of holmium adatom on platinum surface. Within a combination of the density functional theory (DFT) with the exact diagonalization (ED) of Anderson impurity model, the 〈J
z〉 = 0 paramagnetic ground state |J = 8, J
z = ±8〉 is found. In an external magnetic field, this state is transformed to a spin-polarized state with 〈J
z〉 ≈ 6.7. We emphasize the role of 5d–4f interorbital exchange polarization in modification of the 4f shell energy spectrum.
“…It was also proposed that, by combining a particular choice of symmetry, magnetic moment and strong uniaxial anisotropy, the spin can be protected from quantum tunnelling of the magnetization and substrate-driven relaxation 8 9 10 . Experimentally, based on this concept, Miyamachi et al 8 claim to stabilize a single Ho atom on Pt(111).…”
Whether rare-earth materials can be used as single-atom magnetic memory is an ongoing debate in recent literature. Here we show, by inelastic and spin-resolved scanning tunnelling-based methods, that we observe a strong magnetic signal and excitation from Fe atoms adsorbed on Pt(111), but see no signatures of magnetic excitation or spin-based telegraph noise for Ho atoms. Moreover, we observe that the indirect exchange field produced by a single Ho atom is negligible, as sensed by nearby Fe atoms. We demonstrate, using ab initio methods, that this stems from a comparatively weak coupling of the Ho 4f electrons with both tunnelling electrons and substrate-derived itinerant electrons, making both magnetic coupling and detection very difficult when compared to 3d elements. We discuss these results in the context of ongoing disputes and clarify important controversies.
“…More recently, a holmium atom on a platinum (111) surface was found to have a very large total angular momentum of J = 8. 7 . Most of the theoretical understanding relies on the theory of the single-impurity problem 29 and indirect exchange (Ruderman-Kittel-Kasuya-Yosida -RKKY) [30][31][32][33] .…”
We present an extensive study of the two-impurity Kondo problem for spin-1 adatoms on square lattice using an exact canonical transformation to map the problem onto an effective one-dimensional system that can be numerically solved using the density matrix renormalization group method. We provide a simple intuitive picture and identify the different regimes, depending on the distance between the two impurities, Kondo coupling JK , longitudinal anisotropy D, and transverse anisotropy E. In the isotropic case, two impurities on opposite(same) sublattices have a singlet(triplet) ground state. However, the energy difference between the triplet ground state and the singlet excited state is very small and we expect an effectively four-fold degenerate ground state, i.e., two decoupled impurities. For large enough JK the impurities are practically uncorrelated forming two independent underscreened states with the conduction electrons, a clear non-perturbative effect. When the impurities are entangled in an RKKY-like state, Kondo correlations persists and the two effects coexist: the impurities are underscreened, and the dangling spin-1/2 degrees of freedom are responsible for the inter-impurity entanglement. We analyze the effects of magnetic anisotropy in the development of quasi-classical correlations.
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