Doped two orbital chains with strong Hund's rule couplings - Ferromagnetism, spin gap, singlet and triplet pairings

Different models for doping of two-orbital chains with mobile S = 1/2 fermi ons and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the S = I spins are investigated by density matrix renormalization group (DMRG) m ethods. The competition between antiferromagnet;ic (AF) and FM order leads to a rich phase digram with a narrow FM region for weak AF couplings and st rongly enhanced triplet pairing correlations. Without a level difference be tween the orbitals, the spin gap persists upon doping, whereas gapless spin excitations are generated by interactions among itinerant polarons in the presence of a level difference. In the charge sector we find dominant singl et pairing correlations without a level difference, whereas upon the inclus ion of a Coulomb repulsion between the orbitals or with it level difference , charge density wave (CDW) correlations decay slowest. The string correlat ion functions remain finite upon doping for all models.