Many-body theories of inelastic electron tunneling spectroscopy (IETS): Experimental evidence of the inadequacy of the transfer hamiltonian formalism of IETS, interpretation and discussion of alternative theories

Abstract

Recent experiments, by Kirtley and Hansma, in inelastic tunneling spectroscopy (IETS) of the vibrational excitation of molecular impurities trapped in the barrier of a metal-insulator-metal diode exhibited a marked asymmetry with respect to reversal of bias. It is shown that the standard, linear response formulation of the transfer Hamiltonian theory of inelastic tunneling cannot accommodate such an asymmetry. The alternatives to the ad-hoc “golden-rule” type theory proposed by Kirtley, Scalapino, and Hansma of inelastic tunneling are critically reviewed. A new theory based on Feuchtwang's general many-body tunneling theory is developed. It is shown that this theory exhibits all the qualitative features of the golden-rule type analysis. The theory suggests that the differential tunneling conductivity exhibits a more complex structure than predicted by the golden rule. This contrasts with the analysis of Caroli et al., which formally agrees with the results of the golden-rule type theory. It is suggested that the golden-rule type theory of inelastic tunneling may possibly fail to provide a satisfactory phenomenological description of IETS.