Berry phases, pairing symmetry, and nodeless d-wave states in a strongly correlated polaron model

The authors use path integral and exact diagonalization techniques to study the tunneling of dopant-induced hole polarons which are self-localized by electron-phonon coupling in a two-dimensional anti-ferromagnet. Their low-energy dynamics is found to be dominated by 2nd and 3rd neighbor hopping processes which carry a (-1) Berry phase factor and lead to non-s-wave hole pairing symmetries, including possible nodeless dx2-y2 pair wavefunctions. The polarons obey effective spin-1/2-fermion quasi-particle statistics. The nodeless dx2-y2 wave pairing state can exhibit a transition from gapless to fully gapped behavior in its quasi-particle excitation spectrum, without change of pairing symmetry