Relation between flux formation and pairing in doped antiferromagnets - art. no. 184504

We demonstrate that patterns formed by the current-current correlation func tion are landmarks which indicate that spin bipolarons form in doped antife rromagnets. Holes which constitute a spin bipolaron reside at opposite ends of a line (string) formed by the defects in the antiferromagnetic spin bac kground. The string is relatively highly mobile, because the motion of a ho le at its end does not raise extensively the number of defects, provided th at the hole at the other end of the line follows along the same track. Appr opriate coherent combinations of string states realize some irreducible rep resentations of the point group C-4v. Creep of strings favors d- and p-wave states. Some more subtle processes decide the symmetry of pairing. The pat tern of the current correlation function. which defines the structure of fl ux. emerges from motion of holes at string ends and coherence factors with which string states appear in the wave function of the bound state. Condens ation of bipolarons and phase coherence between them puts to infinity the c orrelation length of the current correlation function and establishes the f lux in the system.