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 ρ˜Ps(ω) 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 ρ˜Ps(ω) at this transition.