MOBILITY OF BIPLASMAPOLARONS AND HIGH-TC SUPERCONDUCTIVITY

The mobility of the Frohlich bipolarons is a challenging matter for th e bipolaronic theory of high-T(c) superconductivity. Here we focus our attention on the problem of the effective mass of a bipolaron in a st rongly ionic system (like the new H(igh)T(c)S(uper)C(onductors) are) a nd in the presence of an electron gas. We show that there is a sizeabl e renormalization of the bipolaron mass due to the polarization effect s of both the optical phonons and plasmons. Moreover, we show that the effective mass decreases increasing the density of carriers, because the screening effects become more important. In all cases, the values of the bipolaron effective mass are not greater than some tens of elec tronic masses (m(e)).