Expulsion of charge carriers from quasi-two-dimensional antiferromagnetic structures and formation of spin-liquid droplets in them

Abstract

In antiferromagnetic semiconductors the charge carrier energy decreases, when the long-range magnetic ordering is destroyed. This leads to the fact that in degenerate quasi-two-dimensional semiconductors to which high-TC superconductors belong, both the collinear and canted antiferromagnetic orderings are unstable at arbitrarily small charge carrier density, if the exchange between carriers and localized moments is not very weak. The condition for instability coincides with condition for formation of an electron self-trapped state inside a ferromagnetic region. This means that the antiferromagnetic structure expulses charge carriers into the ferromagnetic phase. An alternative to it is its expulsion into magnetically disordered phase. Then a new type of the carrier self-trapped state realizes when a carrier disorders magnetically a certain region in the antiferromagnet and stabilizes this region by its localization inside it. It corresponds to antiferromagnetic-spinliquid phase separation on the single-electron level. At sufficiently large carrier densities the canted antiferromagnetic structure induced by carriers may be, atleast, relatively stable.