Nacho Pascual

Abstract:

Graphene nanostructures can spontaneously develop intrinsic paramagnetism due to the stabilization of open shell configurations in its electronic structure. Radical states of the conjugated lattice, as singly occupied states, respond to the presence of finite Coulomb correlations by localizing electrons with a net spin polarization. An interesting aspect of such unconventional form of (para)magnetism is that it belongs to the conjugated lattice of graphene. Therefore, it extends for nanometers length scales, and interacts with others with exchange coupling strengths of tens of millielectronvolts. The challenge of fabricating atomically precise graphene nanostructures with custom shapes for localizing spins and tuning their interactons became possible with the development of complex on-surface synthesis strategies [1].

In this presentation, I will show results on spin-hosting nanographenes, including their syntesis routes, their magnetic fingerprints and the origin of such unconventional form of magnetism. We use scanning tunneling microscopy and spectroscopy to detect and spatially localized the spin density by mapping the amplitude of a Kondo resonance [2,3,4,6] or spin excitations [2,5]. The structures we investigated range from the one-dimensional graphene nanoribbons [3,7], where their band structure can be tuned between different symmetry protected topological phases, to zero-dimensional system like triangulene, where robust spin states are found to survive over a metal surface.

[1] Cai, J. et al., Nature 466, 470–473 (2010).

[2] J. Li, S. Sanz, M. Corso, D.J. Choi, D. Peña, T. Frederiksen, J.I. Pascual, Nature Commun. 10, 200 (2019).

[3] N. Friedrich, P. Brandimarte, J. Li, S. Saito, S. Yamaguchi, I. Pozo, D. Pena, T. Frederiksen, A. Garcia-Lekue, D. Sanchez-Portal and J.I. Pascual, Physical Review Letters 125, 146801 (2020)

[4] J. Li, S. Sanz, J. Castro-Esteban, M. Vilas-Varela, N. Friedrich, T. Frederiksen, D. Peña and J.I. Pascual, Physical Review Letters 124, 177201 (2020)

[5] J. Hieulle, S. Castro, N. Friedrich, A. Vegliante, F. Romero Lara, S. Sanz, D. Rey, M. Corso, T. Frederiksen, J.I. Pascual and D. Pena, Angewandte Chemie-International Edition 60, 25224 (2021)

[6] Tao Wang, Alejandro Berdonces-Layunta, Niklas Friedrich, Manuel Vilas-Varela, Jan Patrick Calupitan, Jose Ignacio Pascual, Diego Peña, David Casanova, Martina Corso, Dimas G. de Oteyza. arXiv:2111.15302

[7] J. Li, S. Sanz, N. Merino-Diez, M. Vilas-Varela, A. Garcia-Lekue, M. Corso, D. de Oteyza, T. Frederiksen, D. Pena and J.I. Pascual, , Nature Communications 12, 5538 (2021)