Johannes Jobst1,2, Ferdinand Kisslinger2, Heiko B. Weber2
1Leiden University, Kamerlingh Onnes Laboratorium, 2300 RA Leiden, Netherlands
2Lehrstuhl für Angewandte Physik, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany 

In graphene, as in other two-dimensional materials, quantum corrections like weak localization, electron-electron interaction and Kondo effect cause a logarithmic correction to the conductivity at low temperatures. Hence, it is difficult to pinpoint Kondo physics from resistivity measurements in graphene. We therefore, introduce a refined analysis of magnetoconductance and magnetoresistance in order to disentangle the contributions of different quantum corrections. We present transport experiments and numerical simulations which display this discrimination in perfect samples. When magnetic molecules are added to graphene, however, not only a logarithmic correction to the conductance occurs, which suggests Kondo physics, but also inhomogeneity is introduced. Our thorough evaluation scheme now reveals that the data can be equally well explained by electron-electron interaction corrections in an inhomogeneous sample or by Kondo physics. Therefore, we conclude that, despite our refined analysis, additional spectroscopic information is necessary to unambiguously identify Kondo effect in graphene. 

Johannes Jobst currently works as postdoctoral researcher at Leiden University in the Netherlands in the group of Sense Jan van der Molen. His main focus lies on the understanding of electronic properties of two-dimensional materials. At the moment he is using low energy electron microscopy to study the local potential drop in samples from graphene and other layered materials. He received his Ph.D. in physics from the Friedrich-Alexander-University Erlangen-Nuremberg (FAU) in 2012. There, he studied the transport properties of epitaxial graphene on silicon carbide in the group of Heiko B. Weber. His research focuses on tuning the properties of this material system and studying the graphene-substrate interactions, for example by intercalation or removing the substrate completely. Furthermore, he investigates fundamental quantum corrections like weak localization, electron-electron interaction and Kondo effect. He is a fellow of the cluster of excellence ‘Engineering of Advanced Materials’ in Erlangen and won the Ohm Prize best thesis award.