Effect of pseudogap on the positronium in void

In ceramic high-Tc superconductor (Bi, Pb)₂Sr₂Ca₂Cu₃O₇ the anomalies in temperature dependence τ₂(T)-lifetime of positrons trapped by microvoids are observed in Tc-region V.L. Sedov, S.N. Kuznetsov, O.A. Tsigelnik, N.N. Oleynikov, D.I. Grigorashev, Phys. Lett. A 222 (1996) 455; D. Sanyal, D. Banerjee, U. De, Phys. Rev. B 58 (1998) 15226]. This effect is considered on the basis of the model in which the positrons trapped in microvoids form positronium atoms, interacting with surrounding medium by the processes Ps↔e⁺+e⁻ V.L. Sedov, O.A. Tsigelnik, Phys. Lett. A 332 (2004) 423]. It is shown that the local density of states of the interacting positronium forms the δ-peak near the lower boundary of the gap 2Δ at ω>−Δ. The conclusion was made that the experimentally observed discontinuous increase τ₂ at the transition of the superconducting phase into pseudogap state is the result of the discontinuous increased weight of the peak at this transition.