Agradecimentos: We gratefully acknowledge enlightening discussions with Annette Bussmann-Holder, Jorge Hirsch, Victor Kabanov, Hugo Keller, Ferdinando Mancini, Frank Marsiglio, and RomanMicnas and the support of the Royal Society (London), the UNICAMP visiting professorship program, and ROBOCON (Campinas, Brazil) Ver menos

Abstract: We report analytical and numerical results on the two-particle states of the polaronic t-J(p) model derived recently with realistic Coulomb and electron-phonon (Frohlich) interactions in doped polar insulators. Eigenstates and eigenvalues are calculated for two different geometries. Our results show that the ground state is a bipolaronic singlet, made up of two polarons. The bipolaron size increases with increasing ratio of the polaron hopping integral t to the exchange interaction J(p) but remains small in the whole range 0 <= t/Jp <= 1. Furthermore, the model exhibits a phase transition to a superconducting state with a critical temperature well in excess of 100 K since the small bipolarons are perfectly mobile. In the range t/Jp <= 1, there are distinct charge and spin gaps opening in the density of states, specific heat, and magnetic susceptibility well above T-c Ver menos