The Theory of the Bose Metal

The existence of finite conductivity in low temperature Bosonic systems has long been suspected due to the behavior of, for example, the Cuprates. Several attempts to develop a theory for such behavior have been made, but all have either effectively required arbitrarily many free parameters or resulted in highly unstable states upon including interactions or disorder. Starting with a single-band dispersion exhibiting a line degeneracy in the ground state, we turn on weak quartic interactions and calculate the resulting many-body ground state and low energy dispersion. We find that not only does the degeneracy persist but the resulting system has finite conductivity at finite temperature and an absence of the Meissner effect. Adding weak on-site bounded uniform disorder does not destroy the degeneracy or the resulting behavior. This work constitutes the first and only few-parameter theory for metallic behavior of low temperature Bosons that is robust against interactions and disorder. Therefore, it is the best known minimal model for the Bose metal, and it identifies the metallic behavior as arising from the simple existence of a line degeneracy minimum in the band structure of a system of Bosons.