Anomalous Kondo resonance mediated by semiconducting graphene nanoribbons in a molecular heterostructure

Abstract

Kondo resonances in heterostructures formed by magnetic molecules on a metal require free host electrons to interact with the molecular spin and create delicate many-body states. Unlike graphene, semiconducting graphene nanoribbons do not have free electrons due to their large bandgaps, and thus they should electronically decouple molecules from the metal substrate. Here, we observe unusually well-defined Kondo resonances in magnetic molecules separated from a gold surface by graphene nanoribbons in vertically stacked heterostructures. Surprisingly, the strengths of Kondo resonances for the molecules on graphene nanoribbons appear nearly identical to those directly adsorbed on the top, bridge and threefold hollow sites of Au(111). This unexpectedly strong spin-coupling effect is further confirmed by density functional calculations that reveal no spin–electron interactions at this molecule-gold substrate separation if the graphene nanoribbons are absent. Our findings suggest graphene nanoribbons mediate effective spin coupling, opening a way for potential applications in spintronics.

Reentrant Kondo effect for a quantum impurity coupled to a metal-semiconductor hybrid contact

“…The Kondo physics in graphene results from localized magnetic moments formed at vacancy sites [29][30][31][32] or through the surface deposition of magnetic atoms 33,34 , in which the local density of states may be modified by either disorder 35,36 or by ripples induced by the underlying substrate 34 . Contrasting to the plethora of studies addressing the Kondo state in carbon nanotubes and on bulk graphene, less attention has been devoted to this effect in nanoribbon systems [37][38][39][40] . Depending on the shape of the edges of a graphene nanoribbon, either zigzag or armchair, its density of states near the Fermi level will be that of a semi-metal, for zigzag nanoribbons, owing to the remarkable existence of metallic states localized at its edges, or it could alternate between being semiconducting or metallic, for armchair nanoribbons, depending on its width 41 .…”

The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects

“…The Kondo effect arises from the interaction of a localized spin with conduction electrons of a host metal [1,2]. Using scanning tunnelling spectroscopy (STS), one of its fingerprints, a resonance close to the Fermi energy E F , i. e. at zero bias voltage, has been investigated for metal adatoms [3,4,5,6,7,8,9,10] and adsorbed molecules [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50]. Recent ...…”

Intra- and intermolecular self-assembly of a 20-nm-wide supramolecular hexagonal grid

“…75). A Kondo effect originated from many body interactions between the magnetic moment of Fe(ii) and free electrons from the substrate 38 . As Fe(ii) typically has a higher magnetic moment in comparison with Ru(ii), a stronger Kondo effect is expected for the Fe(ii) centres present in 4 for further differentiation ( Fig.…”