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Publication Citation: Nonequilibrium Theory of Scanning Tunneling Spectroscopy via Adsorbate Resonances: Nonmagnetic and Kondo Impurities

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Author(s): M Plihal; John William Gadzuk;
Title: Nonequilibrium Theory of Scanning Tunneling Spectroscopy via Adsorbate Resonances: Nonmagnetic and Kondo Impurities
Published: February 01, 2001
Abstract: We report on a fully nonequilibrium theory of the scanning tunneling microscopy (STM) through resonances induced by impurity atoms adsorbed on metal surfaces. The theory takes into account the effect of the tunneling current and finite bias on the system and is valid for arbitrary intra-adsorbate electron correlation strength. It is thus applicable to the recent STM experiments on Kondo impurities. We discuss the finite temperature effects and the consequences of atomic scale resolution of the STM for the spectral property of such systems. We find that the tip position affects the resonance lineshapes in two ways. As a function of distance from surface, the lineshapes vary due to the different extent of the adsorbate and metal wavefunctions into the vacuum. However, we do not expect large variations in lineshapes unless the tunneling into the tightly bound adsorbate states is considerable or when nonequilibrium effects are significant. As a function of lateral tip position, lineshapes should not change significantly on length scales of R{double bar}{less than or equal to}10 {Angstrom} under typical experimental conditions when the electrons tunnel into the perturbed bulk conduction states hybridized with the outer shell {italic sp} adsorbate orbitals. Tunneling into surface states on (111) surfaces of noble metals should be important for observation of the resonance at larger distances (> 10 {Angstrom}) and oscillatory variations in the lineshape should develop. This long range behavior has not been resolved in the recent experiments with Kondo impurities. The temperature dependence of the Kondo resonance cannot be deduced directly from the differential conductance as the thermal broadening of the tip Fermi surface produces qualitatively similar effects of comparable and larger magnitude. Careful deconvolution is necessary to extract the temperate dependence of the Kondo resonance. The finite-bias current-induced nonequilibrium effects in tunneling through Kondo impurities should produce characteristic broadening of the resonance in the case of strong hybridization of the discrete state with the STM tip.PACS numbers 61.16.Ch,72.10.Fk
Citation: Physical Review B
Volume: 63
Issue: No. 8
Pages: 23 pp.
Keywords: Kondo effect;resonance tunneling;scanning tunneling microscope;tunneling spectroscopy
Research Areas: Spectroscopy