Kondo Chains of Organic Radicals on Metallic Surfaces: A Model System of Heavy Fermion Quantum Criticality

The spin chains made of organic open-shell radicals represent a platform to explore quantum magnetism. Here we provide an experimental realization of such systems in terms of organic radicals using on-surface synthesis on a Au(111) surface. The spatially resolved differential conductance spectra reveal that the ground state of the organic radicals is a Kramer's doublet that can be modeled by a spin 1/2 degree of freedom, which is entangled with the conduction electrons of the substrate. We find that the spin-spin exchange interactions between the neighboring radicals and the spin-substrate Kondo interaction are competing, resulting in emergent many-body Kondo physics. Using quantum Monte Carlo simulations, we show that a Kondo lattice model of spin chains on a metallic surface accurately reproduces the experimental results. This allows us to interpret experimental results in terms of a Kondo lattice at the quantum critical point. We foresee that the tunability of these systems will pave the way for realizing quantum simulators of heavy Fermion criticality.