Kavli Affiliate: Li Xin Li
| First 5 Authors: Yan Zhao, Kaiyue Jiang, Peng-Yi Liu, Ruoning Li, Jie Li
| Summary:
Quantum manipulation of molecular radical spins provides a crucial platform
for exploring emergent phenomena in many-body systems. Here, we combine
surface-confined synthesis with scanning tunneling microscopy (STM) tip-induced
dehydrogenation to achieve atom-precise engineering of quasi-one-dimensional
porphyrin-based Kondo chains (1-7 units) on Au(111). Key design innovations
leverage large-sized porphyrins to suppress intrachain antiferromagnetic
coupling, while ${Zn}^{2+}$ chelation at porphyrin cores enhances
molecule-substrate interactions to amplify Kondo effect. High-resolution STS
measurements and low-energy effective modeling collectively demonstrate that
${pi}$-radicals at each fused-porphyrin unit form Kondo singlets screened by
conduction electrons. Adjacent singlets develop direct coherent coupling via
quantum-state-overlap-enabled electron tunneling. Crucially, chiral symmetry in
the effective model governs zero-mode distribution-present in odd-length chains
yet absent in even-length chains-which dictates pronounced odd-even quantum
effects in STS spectra of finite chains. Furthermore, geometric control emerges
through conformational distortions modulated by chain fusion width. This
enables directional tuning of the competition between Kondo screening and
magnetic exchange. Tilted single/fused-triple-porphyrin chains weaken spin
exchange through enhanced Kondo coupling, while parallel fused-double-porphyrin
chains suppress Kondo screening via increased spin exchange. This opposing
modulation of Kondo versus exchange interactions establishes an inverse control
paradigm. This work simultaneously resolves the dimensional dependence of
many-body correlations in confined quantum systems and pioneers approaches for
quantum-critical manipulation in molecular spin architectures.
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