Stripes and a two-component interpretation of NMR in cuprates

Based on the experimental fact that the susceptibilities χi(T) and the corresponding Knight shifts Ki(T) (i=c,ab) are linearly related above certain temperature Tχ*(>Tc), one normally draws a conclusion that a single Fermi component is operative. We show that this may not be generally valid. As a counter example we propose a two-component system were the susceptibilities are determined by a universal function f(T). The model consist of a Fermi component h+ and a Bose component B++ with triplet spin localized in CuO5 sites, in chemical equilibrium with respect to reaction B++→2h+, where f(T) gives fraction of bosons and 1-f(T) the fraction fermions. The susceptibilities above T*χ are given by adding the fermion and boson contributions in the form χi(T)=χi0+Ai[1-f(T)]+Bif(T), where χi0, Ai and Bi are T-independent. Clearly then χc(T) and χab(T) are linearly dependent. If the bosons are localized within the CuO6 octahedra or CuO5 pyramids in the ab planes, rows of such tilted sites can explain the occurrence of stripes of localized charge and antiferromagnetic fluctuations in 2D CuO2 planes