Tunable Kondo effect in graphene with defects

• Published in: Nature physics 2011-07, Vol.7 (7), p.535-538
• Main Authors: Chen, Jian-Hao, Li, Liang, Cullen, William G., Williams, Ellen D., Fuhrer, Michael S.
• Format: Article
• Language: English
• Subjects: Atomic; Carbon; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Conduction electrons; Crystal defects; Curvature; Graphene; Graphite; Irradiation; Joining; Kondo effect; letter; Magnetism; Materials science; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Physics; Physics and Astronomy; Theoretical
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1962

Although evidence indicates that defects induce magnetism in graphite, it’s unclear whether this extends to graphene. An observation of the gate-tunable Kondo effect in ion-beam-damaged graphene suggests it does. Graphene is a model system for the study of electrons confined to a strictly two-dimensional layer 1 and a large number of electronic phenomena have been demonstrated in graphene, from the fractional 2 , 3 quantum Hall effect to superconductivity 4 . However, the coupling of conduction electrons to local magnetic moments 5 , 6 , a central problem of condensed-matter physics, has not been realized in graphene, and, given carbon’s lack of d or f electrons, magnetism in graphene would seem unlikely. Nonetheless, magnetism in graphitic carbon in the absence of transition-metal elements has been reported 7 , 8 , 9 , with explanations ranging from lattice defects 10 to edge structures 11 to negative curvature regions of the graphene sheet 12 . Recent experiments suggest that correlated defects in highly-ordered pyrolytic graphite (HOPG), induced by proton irradiation 8 or native to grain boundaries 7 , can give rise to ferromagnetism. Here we show that point defects (vacancies) in graphene 13 are local moments which interact strongly with the conduction electrons through the Kondo effect 6 , 14 , 15 , 16 , providing strong evidence that defects in graphene are indeed magnetic. The Kondo temperature T K is tunable with carrier density from 30 to 90 K; the high T K is a direct consequence of strong coupling of defects to conduction electrons in a Dirac material 16 .