Lecture

Van Marum Colloquium: Magnetic Carbon

• Prof. Thomas Heine (TU Dresden)

Date

Tuesday 5 March 2024

Time

11:00 - 12:00

Location

Gorlaeus Building
Einsteinweg 55
2333 CC Leiden

Room

DM.1.09

Thomas Heine, FRSC, MAE (PhD 1999, venia legendi 2006 TU Dresden) started his research group in 2008 at Jacobs University Bremen, moved in 2015 to University of Leipzig and 2018 to his current position at the School of Science, TU Dresden. He is a highly cited author with more than 350 peer-reviewed articles, an h-index of 90 (ISI) / 101 (Google Scholar).

Prof. Heine is elected member of the Review Board of Deutsche Forschungsgemeinschaft (DFG). He coordinates DFG Priority Program PP 2244 “2D Materials: Physics of van der Waals [hetero]structures”, the DFG Researcher Training Group RTG 2861 “Planar Carbon Lattices”, and the Marie S. Curie European Training Network “2Exciting”.

Abstract

It is generally accepted that carbon is the most versatile element of the periodic table, and it offers a plethora of compounds ranging from biology to materials science. While the list of fascinating properties carbon materials offer is long, they are not yet famous for magnetism.

Indeed, most carbon materials are diamagnetic. Defects, dopants and dangling bonds can introduce paramagnetic centers without the potential to generate magnetic ordering. Recently reported magic-angle twisted bilayer graphene may become ferromagnetic due to a half-filled flat band at the fermi level and spin-orbit coupling [1]. A spectacular early report on magnetic carbon in pressurized fullerenes [2] was found to be caused by defects and the paper has been retracted five years later.

We propose an alternative concept to generate carbon materials with strongly coupled magnetic centers. Our materials are based on molecular triangulene and its derivatives, aromatic molecules intrinsically carrying one or two unpaired electrons. Using covalent linkages that preserve electron conjugation, we construct two-dimensional polymers with honeycomb-kagome lattice. The magnetic coupling between the monomers is facilitated by the linker groups. This has been examined in detail for the dimers [3]. When extending this concept to 2D polymers, we predict magnetic carbon materials with intriguing electronic structure that includes Stoner ferromagnetism with Weyl points at the Fermi level, and Mott-Hubbard insulator antiferromagnetism, which would be the first metal-free ferro- and antiferromagnetic materials with strong magnetic coupling with a Curie/Néel temperature above 250 K [4].

References

1.  A. A. Sharpe E. J. Fox, A. W. Barnard, J. Finney, K. Watanabe, T. Taniguchi, M. A. Kastner, D. Goldhaber-Gordon, ACS Nano 21, 4299 (2021).
2. T. L. Makarova, B. Sundqvist, R. Höhne, P. Esquinazi, Y. Kopelevich, P. Scharff, V. A. Davydov, L. S. Kashevarova, A. V. Rakhmanina, Nature 413, 716, (2001) (retracted).
3.  H. Yu, T. Heine, J. Am. Chem. Soc. 145, 19303 (2023).
4. H. Yu, T. Heine, submitted, arxiv: 2311.09026