Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities

Merino, J. M.; Gunnarsson, O.

doi:10.1103/physrevb.69.115404

Cited by 46 publications

(44 citation statements)

References 22 publications

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“…Second, we neglect the energy dependence of the hopping matrix elements V kη,i = V η,i . 33 These approximations are justified in IETS experiments where the temperature is at most a few kelvins and the applied bias is below 50 mV. If we introduce the excitation energy associated with the transition between n and n states in the q 0 manifold, nn = E n − E n , and we define the average energy¯ ηη nn = 1/2(μ η + μ η + nn ), the transition rates W ηη nn obtained in Appendix B can be expressed as…”

Section: B Master Equation Transition Rates and Currentmentioning

confidence: 99%

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Delgado

Fernández-Rossier

2011

Phys. Rev. B

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We propose cotunneling as the microscopic mechanism that makes possible inelastic electron tunneling spectroscopy of magnetic atoms in surfaces for a wide range of systems, including single magnetic adatoms, molecules, and molecular stacks. We describe electronic transport between the scanning tip and the conducting surface through the magnetic system (MS) with a generalized Anderson model, without making use of effective spin models. Transport and spin dynamics are described with an effective cotunneling Hamiltonian in which the correlations in the magnetic system are calculated exactly and the coupling to the electrodes is included up to second order in the tip MS and MS substrate. In the adequate limit our approach is equivalent to the phenomenological Kondo exchange model that successfully describes the experiments. We apply our method to study in detail inelastic transport in two systems, stacks of cobalt phthalocyanines and a single Mn atom on Cu 2 N. Our method accounts for both the large contribution of the inelastic spin exchange events to the conductance and the observed conductance asymmetry.

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Section: B Master Equation Transition Rates and Currentmentioning

confidence: 99%

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Delgado

Fernández-Rossier

2011

Phys. Rev. B

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“…A lineshape analysis of the bound state indicates that native adatoms decrease the surface-state lifetime, while a cobalt adatom causes no significant change. PACS numbers: 73.20.Fz, 68.37.Ef, 72.15.Qm The unique ability of scanning tunneling microscopy and spectroscopy (STS) to access locally the density of states of single adsorbed atoms and clusters has been recently used to investigate magnetic adatoms which -owing to the Kondo effect -exhibit a sharp spectroscopic structure close to the Fermi energy E F [1,2,3,4,5,6]. Surprisingly, only few studies of metal surfaces have been reported for non-magnetic adatoms and for a wider energy range around the Fermi level [4,7,8,9,10].…”

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Surface-State Localization at Adatoms

et al. 2005

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Low-temperature scanning tunneling spectroscopy of magnetic and non-magnetic metal atoms on Ag(111) and on Cu(111) surfaces reveals the existence of a common electronic resonance at an energy below the binding energies of the surface states. Using an extended Newns-Anderson model, we assign this resonance to an adsorbate-induced bound state, split off from the bottom of the surface-state band, and broadened by the interaction with bulk states. A lineshape analysis of the bound state indicates that native adatoms decrease the surface-state lifetime, while a cobalt adatom causes no significant change. PACS numbers: 73.20.Fz, 68.37.Ef, 72.15.Qm The unique ability of scanning tunneling microscopy and spectroscopy (STS) to access locally the density of states of single adsorbed atoms and clusters has been recently used to investigate magnetic adatoms which -owing to the Kondo effect -exhibit a sharp spectroscopic structure close to the Fermi energy E F [1,2,3,4,5,6]. Surprisingly, only few studies of metal surfaces have been reported for non-magnetic adatoms and for a wider energy range around the Fermi level [4,7,8,9,10]. There is a good reason to explore the physics beyond a narrow range around E F . For instance, it is known that a localized attractive perturbation of a two-dimensional electron gas should result in the appearance of a bound state, split off from the bottom of the continuum, and with a wave function localized around the perturbation [11]. Surface and image-potential states represent an opportunity to investigate this scenario with STS. In fact, it has been predicted that bound states should appear around single alkali atoms on metal surfaces as a consequence of their attractive perturbation on these twodimensional electron gases [12].In this Letter, we present a comparative lowtemperature STS study of a set of adsorbates on the Ag(111) and the Cu(111) surfaces. We show that the density of states (DOS) of single silver and cobalt atoms adsorbed on Ag(111), as well as single copper and cobalt atoms adsorbed on Cu(111), exhibit a resonance below the binding energy E 0 of the surface states of these substrates. Within the framework of a Newns-Anderson model extended to a two-band interaction, we assign this resonance to a bound state split-off from the bottom edge of the surface-state band. A lineshape analysis suggests that the scattering of the surface state at the adsorbate affects its lifetime, depending on the adatom nature. This appears to be a general property of atoms interacting with a two-dimensional electron gas. The measurements were performed in a homebuilt ultrahigh vacuum scanning tunneling microscope at a working temperature of T = 4.6 K. The Ag(111) and the Cu(111) surfaces were cleaned by Ar + sputter/anneal cycles. The single copper and silver adatoms were created by controlled tip-sample contact, whereas the single cobalt atoms were evaporated onto the cold substrates by heating a degassed cobalt wire wound around a pure W wire (> 99.95 %). The evaporation, through an opening of ...

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“…Although there has been considerable effort in describing the adatom/substrate system theoretically it is still unclear whether the lineshape as observed in STS experiments and hence q is determined rather by interfering tunneling channels [18] or by the electronic structure of the substrate [19,20]. Typical tunneling spectra, which we measure with the tip placed above a single cobalt adatom are shown in Fig.…”

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Kondo Temperature of Magnetic Impurities at Surfaces

et al. 2004

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Based on the experimental observation, that only the close vicinity of a magnetic impurity at metal surfaces determines its Kondo behaviour, we introduce a simple model which explains the Kondo temperatures observed for cobalt adatoms at the (111) and (100) surfaces of Cu, Ag, and Au. Excellent agreement between the model and scanning tunneling spectroscopy (STS) experiments is demonstrated. The Kondo temperature is shown to depend on the occupation of the d-level determined by the hybridization between adatom and substrate with a minimum around single occupancy.PACS numbers: 72.10. Fk, 72.15.Qm, 68.37.Ef Understanding the physics of a single spin supported on a metal host is at the basis of a bottom up approach to the design of high density magnetic recording [1]. The effects occuring in the limit of very small magnetic structures can be studied macroscopically on dilute magnetic alloys or microscopically for single magnetic impurities [2,3] and spins in quantum dots [4,5]. These systems develop a rich phenomenology -which is commonly referred to as the Kondo problem [6]. It deals with the interaction of a magnetic impurity with the conduction electrons of a surrounding non-magnetic metal host. This interaction leads to the screening of the spin of the impurity and in consequence to anomalies in the macroscopic properties. A many body ground state is formed at temperatures well below the Kondo temperature T K . Once the Kondo temperature of a given system is known, its behaviour at low temperatures is completely determined. The first experimental evidence became available 70 years ago by measurements of the resistivity of nonmagnetic metals with minute amounts of magnetic impurities [7] which showed an anomalous behaviour below T K . It is only recently, that interest has revived through the investigation of Kondo phenomena in quantum dots on one hand -providing model systems, which allow tuning of the relevant Kondo parameters easily [4,5], and of single magnetic impurities using low temperature scanning tunneling microscopy (STM) and spectroscopy (STS) on the other hand. The spectroscopic signature of the Kondo effect,

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Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities

Cited by 46 publications

References 22 publications

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Cotunneling theory of atomic spin inelastic electron tunneling spectroscopy

Surface-State Localization at Adatoms

Kondo Temperature of Magnetic Impurities at Surfaces

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