Probing magnetic excitations and correlations in single and coupled spin systems with scanning tunneling spectroscopy

Abstract

Spectroscopic measurements with low-temperature scanning tunneling microscopes have been used very successfully for studying not only individual atomic or molecular spins on surfaces but also complexly designed coupled systems. The symmetry breaking of the supporting surface induces magnetic anisotropy which lead to characteristic fingerprints in the spectrum of the differential conductance and can be well understood with simple model Hamiltonians. Furthermore, correlated many-particle states can emerge due to the interaction with itinerant electrons of the electrodes, making these systems ideal prototypical quantum systems. In this manuscript more complex bipartite and spin-chains will be discussed additionally. Their spectra enable to determine precisely the nature of the interactions between the spins which can lead to the formation of new quantum states which emerge by interatomic entanglement. Figure 1: (a) Schematic view of the tunneling process between the electrodes of an idealized tip and sample with their constant densities of states ρt and ρs, respectively: In addition to the elastic tunneling current, an inelastic channel may open at a bias |eV T | ≥ ε i with ε i as the energy difference between the ground and an excited internal state. Under this circumstances an electron crossing the barrier can change its quantum state by losing part of its energy and exciting an internal degree of freedom, for example, the spin orientation of an magnetic adsorbate on the surface. (b) Schematic differential conductance, dI/dV (upper curve) and dI 2 /d 2 V (lower curve), spectra of an inelastic tunneling process. Symmetrically around E F a step like structure at a bias voltage |eV T | = ε i is detected in the dI/dV curve. This is smeared out at non-zero temperature (dashed line) leading to peaks with a width of 5.4k B T in the dI 2 /d 2 V curve. Figure adapted from reference [17].

Observation of Coexistence of Yu-Shiba-Rusinov States and Spin-Flip Excitations

“…S10 for details). 39,40 Comparing the experimental values with the theoretical predictions again highlights the strong correspondence between theory and experiments.…”

“…18,32,[35][36][37][38][39][40] These are associated with the spin-flip (SF) events, whereby the spin projection changes by ±1. 35,39,40 The renormalization of the magnetic anisotropy, associated with the transverse part of the ex- dependence. In the simple picture, the relative magnitudes of these two channels (YSR and spin-flip) are not constrained and, in principle, both of these effects should be observed simultaneously.…”

Sensing the Spin of an Individual Ce Adatom

“…Here, |φ i , Ψ i = |φ i |Ψ i are product states,σ 0 and1 are identity matrices in their corresponding Hilbert subspaces, and U is a Coulomb scattering parameter which arXiv:1908.08267v1 [cond-mat.mes-hall] 22 Aug 2019 -9 -6 -3 0 3 6 9 -9 -6 -3 0 3 6 9 -9 -6 -3 0 3 6 9 -9 -6 -3 0 3 6 9 bias V (mV) accounts not only for a background dI/dV , but also leads to interference induced bias asymmetries in the spectra, when higher scattering orders are considered [26]. We find an excellent fit to the Fe data using the previously found effective spin S = 2, easy-axis anisotropy (D < 0) which favors the high magnetic moment along the N-rows of the Cu 2 N [25], and a transport model which includes scattering processes up to 3 rd order in the matrices [26,27] (Fig. 1d).…”

Enhanced lifetimes of spin chains coupled to chiral edge states

“…The spin lifetime of individual magnetic atoms is controlled by the electronic properties of the substrate, the surface spin system, and their exchange interaction, encoded in ρJ, where J is the Kondo exchange and ρ is the substrate density of states [12][13][14]. The enhancement of spin-lifetimes by reduction of either ρ or J has been has been explored in several systems, including heavy metal substrates with strong spin-orbit [15], superconducting [16] or semiconducting [3] surfaces and thin decoupling layers, such as Al 2 O 3 on NiAl [1], Cu 2 N on Cu(100) [17] or MgO/Ag(100) [18].…”