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O: Fachverband Oberflächenphysik
O 51: Focus Session: Molecular Nanostructures on Surfaces: On-Surface Synthesis and Single-Molecule Manipulation II
O 51.2: Talk
Wednesday, March 20, 2024, 15:30–15:45, HE 101
Polyradical State of an Extended Aza-Triangulene — •Francisco Romero-Lara1, Alessio Vegliante1, Manuel Vilas-Varela2, Hector Briongos1, Niklas Friedrich1, Dongfei Wang1, Ricardo Ortiz3, Patrick Calupitan3, Fabian Schulz1, Thomas Frederiksen3, Diego Peña2, and Jose Ignacio Pascual1 — 1CIC nanoGUNE, Donostia, Spain — 2CiQUS, Santiago de Compostela, Spain — 3DIPC, Donostia, Spain
Triangulene nanographenes are the most paradigmatic case for the emergence of spin states due to the frustration of the bipartite lattice of graphene. Increasing their size implies an increase in sublattice imbalance, resulting in a larger spin state according to Lieb's theorem. Another way of controlling the spin state is by heteroatom substitution, e.g. N reduces the spin state by 1/2. In this work, we show that, by increasing the size of an aza-[3]-triangulene but maintaining the sublattice imbalance, the interplay between electron correlations and wavefunction hybridization is modified, resulting in a polyradical state. The successful synthesis of this extended triangulene on a Au(111) surface is confirmed by STM and nc-AFM with CO tips. We use STS to prove the magnetic character of the nanographene by measurements of the Kondo effect and spin excitations. Temperature and magnetic field dependence of the Kondo resonance indicates an S=1/2 ground state. Simultaneously, a spin excitation to a S=3/2 excited state was observed. These findings support the presence of a polyradical state in this nanographene conformed by three antiferromagnetically aligned radicals, in agreement with multireference CAS theoretical methods.
Keywords: Scanning Tunneling Microscopy; On-surface synthesis; Nanographenes; Spin states; Kondo effect