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O: Fachverband Oberflächenphysik

O 77: Gerhard Ertl Young Investigator Award Competition

O 77.4: Talk

Thursday, March 21, 2024, 12:00–12:30, HE 101

Investigating many-body phenomena through molecular nanostructures — •Shantanu Mishra — IBM Research Europe - Zurich, 8803 Rüschlikon, Switzerland

This two-part contribution shows that individual organic molecules and molecular nanostructures on surfaces serve as an outstanding material platform to access many-body physics. In the first part, the tip-induced synthesis of an elusive organic molecule, namely indeno[1,2-a]fluorene, will be demonstrated on thin insulating NaCl films on (111) coinage metal surfaces [1]. The molecule exhibits ground state bistability, wherein it can be stabilized either in a (high-spin) open-shell state, or a (low-spin) closed-shell state, each of which shows characteristic experimental bond length alternation and frontier orbital densities that agrees with theory. Switching between open- and closed-shell states of an individual molecule is observed by changing its adsorption site on NaCl. In the second part, the on-surface synthesis of organic S = 1 antiferromagnetic quantum spin chains on Au(111) surface will be shown [2]. A systematic study of length-dependent magnetic excitations in both open-ended and cyclic spin chains reveal gapped spin excitations in the bulk, with the gap saturating for sufficiently long spin chains, and fractional S = 1/2 edge states at the chain termini, which manifest as Kondo resonances. It will be shown that these spectral features are direct evidence of emergent symmetry-protected topological order in the spin chains, ratifying Haldane's conjecture for integer-spin antiferromagnetic chains. [1] S. Mishra et al. arXiv:2303.04483 (2023). [2] S. Mishra et al. Nature 598, 287 (2021).

Keywords: on-surface synthesis; scanning tunneling microscopy; atomic force microscopy; tip-induced chemistry; open-shell molecules