  We consider a 2-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 correlations with
Kondo spin screening stabilizes a metallic spin-liquid phase of the localized
spins without geometric frustration. For weak Kondo coupling the spin liquid
and the Kondo singlet phase 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 near a spin-density wave instability.
