Strongly correlated pi-magnets driven by e-ph and e-e interaction

Recent progress in on-surface chemistry enabled the synthesizing and characterizing of novel-conjugated carbon molecules with magnetic properties systems with unprecedented properties [1]. This route, complemented with high-resolution scanning probe imaging (SPM), provides new opportunities to understand their chemical and physical properties, including the emergence of magnetism in such materials [2].

In the first part of the talk, we will discuss the connection between the topological band structure of -conjugated polymer introduced in the framework of the Su-Schrieffer-Heeger (SSH) model and their conjugation.  We will discuss the quantum phase transition between two topologically distinct phases in a π-conjugated polymer [3]. This quantum phase transition is defined by the length of the polymer, triggered by the transition from topologically trivial to a non-trivial phase above a certain polymer length. We demonstrate that pseudo Jahn-Teller effect is the driving mechanism responsible for the quantum phase transition [4].

In the second part, we will present a synthesis of polyradical molecules with strong multireference character. Their electronic structure is analyzed using the SPM technique, including nickelocene functionalized probes and many-body CAS calculations, enabling us to properly describe the multireference states [5]. We will discuss a PAH molecule, where a strongly entangled tetra radical character is introduced by a combination of the e-e interaction and the frustrated topology. We will also discuss the effect of the pentagon defects on the electronic structure and the coexistence of underscreened Kondo and spin excitation in defective molecules, whose origin will be rationalized as a consequence of multiconfigurational spin-flip scattering between unpaired electrons of the molecule and the electronic bath of a metallic surface [6].

[1] J.Li et al., Nature Communication 10, 200 (2019); N. Pavlicek et al., Nature Nanotechnology 12, 308 (2017); S. Mishra et al., Nature Nanotechnology 15, 22 (2019).

O. Gröning, et al., Nature 560, 209 (2018); D.J. Rizzo, et al., Nature 560, 204 (2018)

[2] R. Ortiz et al., Nano Letters 19, 5991 (2019).

[3] B. Cierra et al, Nature Nano, 15, 437 (2020)

[4] H. Gonzalez-Herroro et al Adv. Mat. 33, 2104495 (2021)

[5] S. Song et al. Nature Chem 16, 938 (2024)

[6] A. Calvo-Fernandez arXiv:2405.15958 [