Scanning tunneling spectroscopic evidence of crossover transition in the two-impurity Kondo problem

Abstract

To explore the crossover transition in the two-impurity Kondo problem, we calculate the differential conductance (d I / d V) corresponding to scanning tunneling spectroscopy (STS) measurements of a magnetic dimer adsorbed on a metal surface covered by a decoupling layer. With the aid of the numerical renormalization group (NRG) technique, we find that the peak structure of the d I / d V spectra near the Fermi level changes gradually as a function of the adatom separation and the coupling between the adatom localized spins and the metal surface conduction band. When the coupling becomes small, the peak disappears and, instead, a dip structure appears near the Fermi level. This dip structure is the manifestation of the strong antiferromagnetic correlation between the localized spins. We conclude that the gradual change of the d I / d V structure from a peak structure to a dip structure is an evidence of the crossover transition in the two-impurity Kondo problem.