Competition of superfluidity and density waves in one-dimensional Bose-Fermi mixtures

We study a mixture of one-dimensional bosons and spinless fermions at incommensurate filling using phenomenological bosonization and Green's function techniques. We derive the relation between the parameters of the microscopic Hamiltonian and macroscopic observables. Galilean invariance results in extra constraints for the current-current interactions. We obtain the exact exponents for the various response functions, and show that superfluid fluctuations are enhanced by the effective boson-fermion density-density interaction and suppressed by the effective boson-fermion current-current interaction. In the case of a bosonized model with purely density-density interaction, when the effective boson-fermion density-density interaction is weak enough, the superfluid exponent of the bosons has a nonmonotonic variation with the ratio of the fermion velocity to the boson velocity. In contrast, the density-wave exponent and the exponent for fermionic superfluidity are monotonic functions of the velocity ratio.