Co adatoms on Cu surfaces: Ballistic conductance and Kondo temperature

Abstract

The Kondo zero bias anomaly of Co adatoms probed by scanning tunneling microscopy is known to depend on the height of the tip above the surface, and this dependence is different on different low index Cu surfaces. On the (100) surface, the Kondo temperature first decreases then increases as the tip approaches the adatom, while on the (111) surface it is virtually unaffected. These trends are captured by combined density functional theory and numerical renormalization group (DFT+NRG) calculations. The adatoms are found to be described by an S = 1 Anderson model on both surfaces, and ab initio calculations help identify the symmetry of the active d orbitals. We correctly reproduce the Fano lineshape of the zero bias anomaly for Co/Cu(100) in the tunneling regime but not in the contact regime, where it is probably dependent on the details of the tip and contact geometry. The lineshape for Co/Cu (111) is presumably affected by the presence of surface states, which are not included in our method. We also discuss the role of symmetry, which is preserved in our model scattering geometry but most likely broken in experimental conditions.

Kondo Resonance of a Co Atom Exchange Coupled to a Ferromagnetic Tip

“…Here, we use a nickel tip to contact an individual Co atom adsorbed on a Cu(100) surface (see inset of nized to be a spin-1/2 Kondo system [30,31]. We show that the ferromagnetic exchange coupling between the tip-apex atom and the Co atom inherent to our contact measurement promotes a reproducible asymmetric spin-split Kondo resonance.…”

“…With Cu tips, a single peak-like resonance is detected, the Frota-Fano fits yielding q ≫ 1. The resonance width also increases monotonically when decreasing the tip-Co distance due to tip-induced modifications of the Co adsorption on Cu(100) [29,30]; the corresponding Kondo temperatures extracted from the fits are shown in Fig. 2c and reach values of 200 K at z = −0.6Å (higher tip excursions can result in tip instabilities).…”

Two-Orbital Kondo Screening in a Self-Assembled Metal–Organic Complex

“…It is interesting to note that Fe atoms buried by the molecules have S = 1 with two singly occupied orbitals, as Co atoms on Cu(111). 43 However, in the case of Co/Cu(111), the two orbitals are degenerate, resulting in a single value for T K .To investigate the degree of screening of both Kondo channels, we performed X-ray absorption spectroscopy (XAS) and XMCD measurements at the EPFL/PSI X-Treme beamline at the Swiss Light Source. 44 Since the Fe deposition temperature controls the Fe abundance in the three adsorption sites on the (NC-Ph 3 -CN) 3 Cu 2 /Cu(111) surface, we can produce samples with the Fe adatoms predominantly adsorbed on the substrate (sample A, T dep = 3 K) and samples where they are mostly below the molecules (sample B, T dep = 40 K).…”

Kondo-Fano resonance in atomic-scale contacts for ferromagnetic metals

“…The importance of the spatial geometry for the conductance is also pointed out by theoretical studies [15,16]. For instance, in Co adatom on the Cu(100) surface, the zero-bias anomaly due to Fano resonance appears in terms of the interference between the s and d z 2 orbitals [16].…”

“…For instance, in Co adatom on the Cu(100) surface, the zero-bias anomaly due to Fano resonance appears in terms of the interference between the s and d z 2 orbitals [16]. …”