SPECTATOR FERMION BINDING OF BOSONS

We consider a two-component mixture of charged fermions on neutralizing background with all sign combinations and arbitrarily small mass ratios. In the two-impurity limit for the heavier component we show that the pair forms a bound state for all charge combinations. In the lowest order approximation we derive a closed-form expression for V-eff(r), the binding potential which has short-range repulsion followed by attraction. In the classical limit, when the mass of embedded particles is large, m(2) much greater than m, we can calculate from V-eff(r) also the cohesive energy E and the bond length R of a metallic crystal such as lithium. For lithium metal the lowest-order result is R = 3.1 Angstrom, E = -1.8 eV, while the corresponding experimental values are 3.4 Angstrom and -1.6 eV. The same interaction for two holes on a parabolic band with m(2) > m gives the quantum mechanical bound state which one may interpret as a boson or local pair in the case of high-T-c and heavy-fermion superconductors.