Magnetic adatoms as memory bits: A quantum master equation analysis

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 that in general it cannot be reduced to a classical master equation in the basis of the unperturbed crystal-field Hamiltonian. Rather, depending on parameters and control fields, "environment induced superselection" principles choose the appropriate set of basis states, which in turn determines the specific relaxation channels and lifetimes. Our simulations suggest that in ideal situations the lifetimes should be even longer than observed in the experiment. We, therefore, investigate the influence of various perturbations. We also study the initialization process of the state of the Ho atom by applied voltage pulses and conclude that fast, high fidelity preparation, on a $100\,\text{ns}$ timescale, should be possible.Comment: 14 pages, 11 figure

Magnetic character of holmium atom adsorbed on platinum surface

“…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.…”

Absence of a spin-signature from a single Ho adatom as probed by spin-sensitive tunneling

“…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).…”

Spin-1 two-impurity Kondo problem on a lattice

“…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] .…”