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Séminaire Exceptionnel

Vendredi 18 mars à 10h00,
Salle Remy Lemaire, K223

Atomic-scale control of graphene magnetism using hydrogen atoms
I. Brihuega 1,2
1Dept. de Física de la Materia Condensada, Universidad Autónoma de Madrid, Spain
2Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Spain.

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Incorporating magnetism to the long list of graphene capabilities has been pursued since its first isolation in 2004. From a theoretical point of view, the basics to induce magnetic moments in graphene are rather simple : removing a single pz orbital from the π -graphene system leaves an unpaired electron giving rise to a half-filled π-state at the Fermi energy (EF). A magnetic moment then emerges due to electron-electron repulsion U taking place in this induced state. Thus, isolated hydrogen atoms absorbed on graphene are predicted to induce local magnetic moments. Direct observation of these magnetic moments and their interactions as well as their manipulation still remains a major experimental challenge.
In this talk I will show how we use a scanning tunneling microscope to explore and manipulate graphene π-magnetism at an atomic level. Our work shows how the absorption of single H atoms on graphene magnetizes the graphene regions around them. In contrast to common magnetic materials, where the magnetic moments are localized in a few angstroms, the induced graphene magnetic moments extend over several nanometers and present an atomically modulated spin texture. Our measurements also prove that the induced magnetic moments couple strongly at very long distances following a particular rule : magnetic moments sum-up or neutralize critically depending on the relative H-H adsorption sites [1].

Fig. 1. Left, STM topography of a single H atom chemisorbed in graphene. Right, STS measurements of the LDOS induced by the H atom, showing the appearance of a fully polarized peak at EF, and of graphene.

1. H. González-Herrero, J. M. Gómez-Rodríguez, P. Mallet, M. Moaied, J. J. Palacios, C. Salgado, M. M. Ugeda, J.Y. Veuillen, F. Yndurain and I. Brihuega, submitted.

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