We report the presence of spin dimerization in the ground state of the one-dimensional Kondo lattice model at quarter filling. The emergence of this new phase of the Kondo lattice can be traced to the form of the RKKY interaction between the localized moments and provides the first example of dimerization induced indirectly by itinerant electrons. We propose this dimer ordering as the driving mechanism of the spin-Peierls phase observed in the quasi-one-dimensional organic compounds $(\mathrm{P}\mathrm{e}\mathrm{r}{)}_{2}M(\mathrm{m}\mathrm{n}\mathrm{t}{)}_2$ ($M=\mathrm{P}\mathrm{t}$, Pd). Moreover, this suggests that a richer phase diagram than the Doniach paradigm may be needed to accommodate the physics of heavy fermion materials.

• Received 26 September 2002

DOI:https://doi.org/10.1103/PhysRevLett.90.247204