Impurity and electronic phase separation in high-T C superconductors and other quasi-two-dimensional degenerate magnetic semiconductors

Both electronic phase separation occuring at impurity frozen, and the impurity phase separation occuring at mobile impurity are investigated for the case of quasi-two-dimensional degenerate magnetic semiconductors to which HTSC's belong. The optimum geometry for the electronic phase separated state is found, and its energy is evaluated. According to these evaluations, the electronic phase separation is not forbidden for HTSC's. The impurity phase separation is calculated with the aid of the jellium model for the impurity metal generalized for the two-dimensional case. At realistic parameters both the impurity-magnetic phases arising as a result of phase separation may be high-conducting or even superconducting.