Quantifying the leading role of the surface state in the Kondo effect of Co/Ag(111)

M. Moro-Lagares, J. Fernández, P. Roura-Bas, M. R. Ibarra, A. A. Aligia, and D. Serrate

Phys. Rev. B 97, 235442 – Published 26 June 2018

Abstract

Using a combination of scanning tunneling spectroscopy and atomic lateral manipulation, we obtained a systematic variation of the Kondo temperature $T_{K}$ of Co atoms on Ag(111) as a function of the surface-state contribution to the total density of states at the atom adsorption site $ρ_{s}$ . By sampling the $T_{K}$ of a Co atom on positions where $ρ_{s}$ was spatially resolved beforehand, we obtain a nearly linear relationship between the magnitudes. We interpret the data on the basis of an Anderson model including orbital and spin degrees of freedom [SU(4)] in good agreement with the experimental findings. The fact that the onset of the surface band is near the Fermi level is crucial to finding the observed linear behavior. In light of this model, the quantitative analysis of the experimental data evidences that at least a quarter of the coupling of Co impurities with extended states takes place through the hybridization to surface states. This result is of fundamental relevance in the understanding of Kondo screening of magnetic impurities on noble-metal surfaces, where bulk and surface electronic states coexist.

Received 6 March 2018
Revised 31 May 2018

DOI:https://doi.org/10.1103/PhysRevB.97.235442

Physics Subject Headings (PhySH)

Kondo effect Surface states

Nanostructures

Multichannel Anderson model Scanning tunneling microscopy Surface scattering

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Moro-Lagares^1,2,3, J. Fernández⁴, P. Roura-Bas⁴, M. R. Ibarra^1,5, A. A. Aligia^4,*, and D. Serrate^1,5,†

¹Instituto de Nanociencia de Aragón, Laboratorio de Microscopias Avanzadas, University of Zaraqoza, E-50018 Zaragoza, Spain
²Institute of Physics, Academy of Sciences, 18221 Prague, Czech Republic
³Regional Centre of Advanced Technologies and Materials, Faculty of Science, Department of Physical Chemistry, Palacky University, 78371 Olomouc, Czech Republic
⁴Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica, 8400 Bariloche, Argentina
⁵Departamento Física Materia Condensada, University of Zaraqoza, E-50018 Zaragoza, Spain

^*aligia@cab.cnea.gov.ar
^†serrate@unizar.es

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 97, Iss. 23 — 15 June 2018

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Left: scheme of the splitting of the (one-particle) $3 d$ orbitals under the point group $C_{3 v}$ . Right: scheme of the splitting of the four antibonding states of symmetry $E$ by the Coulomb repulsion. $ɛ_{F}$ denotes the position of the Fermi energy compatible with the position of the observed Fano antiresonance.
Reuse & Permissions
Figure 2
(a) Representative raw $d I / d V$ $[G_{K} (V)$ , open circles] showing the Kondo zero-bias feature at the center of a single Co atom and background estimation $[G_{0} (V)$ , solid line]. (b) Fit of the resulting $g_{K} (V)$ to Eq. (7), yielding $T_{K} = 56.1 \pm 0.9$ K, $q = 0$ , and $ω_{K} = 7.39 \pm 0.04$ meV. (c) Dispersion found in the Kondo resonance of a set of atoms spread on Ag(111) with the corresponding fit and $T_{K}$ value. (d) Kondo temperature and (e) $q$ factor statistics. Using a Gaussian distribution profile (dashed line) for the $T_{K}$ histogram, we obtain $〈 T_{K} 〉 = 52.1 \pm 9.4$ K.
Reuse & Permissions
Figure 3
(a) Representation of the experiment carried out in the study of the variations of the Kondo resonance with the point contact $ρ_{s}$ . (b) The $d I / d V$ spectrum (circles) and fit to Eq. (7) of the Co atom at the $a$ position (green), $b$ position (red), and $a^{'}$ position (blue). The $a^{'}$ position is the same as the $a$ position after atomic manipulation.
Reuse & Permissions
Figure 4
$T_{K}$ and $A_{K}$ variations with $G (R)$ . (a) STM image of Co/Ag(111) after Co deposition. (b) Co atoms are removed from the working area to avoid their influence on $G$ . (c) Inset: constant-height $G (R) = d I / d V$ map taken at $V = 3$ mV ( $I_{0} = 200$ pA, $V_{0} = - 100$ mV, and $V_{\mod} = 1$ mV). (d) Co atom relocated at a certain position over the surface. (e) Experimental dependence of $T_{K} / 〈 T_{K} 〉$ on the normalized local tunneling conductance $G / G_{0}$ . (f) Experimental dependence of $A_{K}$ on $G / G_{0}$ . In (e) and (f), the color code represents data sets taken with the same tip, while for the same color, the open and solid diamonds distinguish data sets at two different close working areas. All measurements were taken in constant-height mode at $T = 1.1$ K ( $I_{0} = 42$ pA, $V_{0} = - 100$ mV, and $V_{\mod} = 0.5$ mV). (g) Theoretical dependence of $T_{K} / 〈 T_{K} 〉$ on $ρ_{s} / ρ_{s}^{0}$ for different values of $Δ_{s}^{0} / Δ_{b}$ . The dashed lines are linear fits in the region $0.5 < T_{K} / 〈 T_{K} 〉 < 1.5$ . The region enclosed within the dotted rectangle corresponds to the experimental parameter range.
Reuse & Permissions
Figure 5
Differential conductance as a function of voltage. Open circles: experimental $g_{k}$ [the same as Fig. 2] without background. Red line: theory for $Δ_{s} = 69.26$ meV, $Δ_{b} = 256.5$ meV, $p_{b} = 1.16$ , and $p_{d} = 7$ .
Reuse & Permissions
Figure 6
Same as Fig. 4 using Eq. (9). $T_{K}^{0}$ is the value obtained for the same parameters as before and differs from the value of $〈 T_{K} 〉$ by a factor of $\sim 2$ . The region enclosed within the dotted rectangle corresponds to the experimental parameter range.
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics