Construction of Kondo Chains by Engineering Porphyrin {\pi}-Radicals on Au(111)

TL;DR

This study demonstrates the atom-precise construction of porphyrin-based Kondo chains on Au(111) and explores their many-body quantum phenomena, revealing odd-even effects and tunable Kondo interactions in molecular spin systems.

Contribution

It introduces a surface-confined synthesis method combined with STM-induced dehydrogenation to engineer and study Kondo chains at the atomic scale, revealing new quantum effects.

Findings

Odd-length chains exhibit zero-modes due to chiral symmetry.

The number of chains non-monotonically affects Kondo screening.

Wave-function overlap and energy gaps govern many-body interactions.

Abstract

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). 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, the number of parallel porphyrin chains non-monotonically tunes the competition between the Kondo effect and spin exchange, showing opposing trends in strength and demonstrating that both wave-function overlap and the SOMO-LUMO gap collectively govern these interactions. 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.