Quantum Critical Transition and Kondo Screening of Magnetic Moments in Graphene

Jinhai Mao, Yuhang Jiang, Po-Wei Lo, Daniel May, Guohong Li, Guang-Yu Guo, Frithjof Anders, Takashi Taniguchi, Kenji Watanabe, Eva Y. Andrei

Published 2017-11-19Version 1

Pristine graphene is non-magnetic. However when its perfect honeycomb lattice is disrupted by vacancies, graphene develops robust local magnetic moments hosted at the vacancy sites. Here we report on emergent magnetic properties arising from the interaction of the vacancy spins with the conduction electrons. Using scanning tunneling microscopy (STM) and spectroscopy (STS), and numerical renormalization group (NRG) calculations, we find that the conduction electrons can screen the local moment through the formation of an entangled state known as a Kondo screening cloud. Identifying Kondo screening of the vacancy spin by its spectroscopic signature, we detect and map the existence of a quantum phase transition separating magnetic from non-magnetic states. Furthermore, using the unique properties of this phase transition we demonstrate that the local magnetic moment can be controlled with either a gate voltage or through the local curvature of the graphene membrane.