Light bipolarons stabilized by Peierls electron-phonon coupling

It is widely accepted that phonon-mediated high-temperature superconductivity is impossible at ambient pressure, because of the extremely large effective masses of the polarons/bipolarons at strong electron-phonon coupling. Here we challenge this belief by showing that strongly bound yet very light bipolarons appear for strong Peierls/Su-Schrieffer-Heeger coupling in one-dimensional systems. Apart from being light, these bipolarons show a host of unconventional properties, for example at strong coupling there are two bipolaron bands which are stable against strong on-site Hubbard repulsion. Using numerical simulations and analytical arguments, we show that these properties result from the unusual form of the phonon-mediated interactions, which are of “pair- hopping” type instead of regular density-density interactions. These unusual properties of the bipolarons should have non-trivial consequences on the superconducting state expected to arise at finite carrier concentrations, in particular on its critical temperature.