Quantum spin liquid in an RKKY-coupled two-impurity Kondo system

We consider a two-impurity Kondo system with spin-exchange coupling within the conduction band. Our numerical renormalization group calculations show that for strong intraband spin correlations the competition of these nonlocal correlations with local Kondo spin screening stabilizes a phase exhibiting features of a metallic quantum spin liquid, namely nonlocal impurity-spin entanglement and fractionalized charge excitations, without the need for geometric frustration. For weak Kondo coupling, the spin-liquid-like and the Kondo singlet phases are separated by two quantum phase transitions and an intermediate RKKY spin-dimer phase, while beyond a critical coupling they are connected by a crossover. The results suggest how a quantum spin liquid may be realized in heavy-fermion systems with strong magnetic correlations in the conduction band, e.g., near a spin-density-wave instability.