Spin-polarized tunneling microscopy and the Kondo effect

Patton, Kelly R.; Kettemann, Stefan; Zhuravlev, A. K.; Lichtenstein, A. I.

doi:10.1103/physrevb.76.100408

Cited by 19 publications

(29 citation statements)

References 28 publications

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“…For magnetic fields exceeding this energy the Kondo resonance splits. However, the spinresolved properties of this split Kondo state and, in particular, the amount of spin polarization of the two resulting peaks remains elusive [9,10]. While there is one spin-resolved measurement of a split Kondo state [11], the asymmetry of the peaks was not studied systematically and a comprehensive picture is missing.…”

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Spin Polarization of the Split Kondo State

et al. 2015

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Spin-resolved scanning tunneling microscopy is employed to quantitatively determine the spin polarization of the magnetic field-split Kondo state. Tunneling conductance spectra of a Kondo-screened magnetic atom are evaluated within a simple model taking into account inelastic tunneling due to spin excitations and two Kondo peaks positioned symmetrically around the Fermi energy. We fit the spin state of the Kondo-screened atom with a spin Hamiltonian independent of the Kondo effect and account for Zeeman splitting of the Kondo peak in the magnetic field. We find that the width and the height of the Kondo peaks scales with the Zeeman energy. Our observations are consistent with full spin polarization of the Kondo peaks, i.e., a majority spin peak below the Fermi energy and a minority spin peak above. The Kondo effect was discovered experimentally nearly one century ago and starting from the 1960s theory has been employed to unravel its origin and properties [1]. It arises from the screening of a localized magnetic moment by host electrons, which leads to a Fermi-level resonance in the density of states. Kondo physics in the absence of a magnetic field has been studied extensively [2,3], whereas the precise behavior of the Kondo state in a magnetic field is less studied [4][5][6][7][8]. The coupling of the localized spin to the environment sets the relevant energy scale which is typically referred to as Kondo temperature T K . For magnetic fields exceeding this energy the Kondo resonance splits. However, the spinresolved properties of this split Kondo state and, in particular, the amount of spin polarization of the two resulting peaks remains elusive [9,10]. While there is one spin-resolved measurement of a split Kondo state [11], the asymmetry of the peaks was not studied systematically and a comprehensive picture is missing.The Kondo effect of a single atom or molecule on a surface can be probed with scanning tunneling spectroscopy (STS) [3]. When the localized spin is only weakly coupled to the conduction electrons of the substrate a perturbative description can be used [12] and a logarithmic peak at the Fermi energy is detected [13]. For stronger hybridization the arising correlations lead to a change in the density of states [6], which is typically described by a Lorentzian or a Frota function [14]. An additional linear tunnel channel gives rise to interference between different paths, leading to an asymmetric, Fano-like, line shape [15,16]. Systems with a spin S > 1=2 can show the Kondo effect when the magnetocrystalline anisotropy leads to a degenerate m ¼ AE1=2 ground state [5]. Then the resonance at zero bias is accompanied by steps in the tunnel spectra due to inelastic electron tunneling that excites the spin at finite energy. Inelastic tunnel spectroscopy has been employed to investigate such spin excitations in single atoms, molecules, and small clusters on ultrathin insulating layers, semiconductors, and metals [5,[17][18][19][20][21].In this Letter we quantitatively determine the spin polarization of...

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Spin Polarization of the Split Kondo State

et al. 2015

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“…In this way, the local electronic structure of individual transition-metal impurities, having different d-level configurations on a Au surface, was appropriately reproduced. 6 In the Ti/Ag(100) system, we now find that the line shape of the measured conductance reflects electronic characteristics of the metal surface modified by the presence of the magnetic atom due to a non-negligible tipsubstrate interaction, [12][13][14][15][16] whereas, in the case of Ti/Au(111), the interaction atom surface prevails, and the conductance line shape is only determined by the projected density of states on the Ti-atom impurity.…”

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confidence: 76%

Conductance through a Ti-atom impurity in Ag(100) and Au(111): An ionic model considering spin fluctuations

2013

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We describe the interaction between a transition-metal atom and a noble-metal surface by using an ionic model in which the first Hund's rule determines the filling of the atom's d levels, and spin fluctuations occur due to the electron exchange between the metal band and the atom states. We apply our model to the case of adsorbed Ti atoms on noble-metal surfaces (Ag and Au) in which conductance measurements in scanning tunneling microscope experiments suggest a mixed-valence regime according to the position and width of the atomic resonance. By introducing, in our calculation, these two parameters as extracted from the experiment, we satisfactorily reproduce the experimental results in both cases. We find, in the Ag(100) surface, that the conductance spectrum reflects electronic characteristics of the metal surface modified by the presence of the magnetic atom; whereas, in the Au(111) case, only the projected density of states on the Ti atom determines the conductance spectrum shape.

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“…5,20,21 If the tip is ferromagnetic the Fano-Kondo line shape becomes spindependent 22 and the setup can be used as a powerful spin filter. 23 Here, we study spin-dependent transport in a system composed of a ferromagnetic (FM) STM tip coupled to both an adsorbed atom and a host nonmagnetic (NM) surface.…”

Section: Introductionmentioning

confidence: 99%

Scanning tunneling microscope operating as a spin diode

et al. 2011

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We theoretically investigate spin-polarized transport in a system composed of a ferromagnetic scanningtunneling-microscope (STM) tip coupled to an adsorbed atom (adatom) on a host surface. Electrons can tunnel directly from the tip to the surface or via the adatom. Since the tip is ferromagnetic and the host surface (metal or semiconductor) is nonmagnetic we obtain a spin-diode effect when the adatom is in the regime of single occupancy. This effect leads to an unpolarized current for direct bias (V > 0) and polarized current for reverse (V < 0) bias voltages, if the tip is nearby the adatom. Within the nonequilibrium Keldysh technique we analyze the interplay between the lateral displacement of the tip and the intra adatom Coulomb interaction on the spin-diode effect. As the tip moves away from the adatom the spin-diode effect vanishes and the currents become polarized for both V > 0 and V < 0. We also find an imbalance between the up and down spin populations in the adatom, which can be tuned by the tip position and the bias. Finally, due to the presence of the adsorbate on the surface, we observe spin-resolved Friedel oscillations in the current, which reflects the oscillations in the calculated local density of states (LDOS) of the subsystem surface + adatom.

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Spin-polarized tunneling microscopy and the Kondo effect

Cited by 19 publications

References 28 publications

Spin Polarization of the Split Kondo State

Spin Polarization of the Split Kondo State

Conductance through a Ti-atom impurity in Ag(100) and Au(111): An ionic model considering spin fluctuations

Scanning tunneling microscope operating as a spin diode

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