Mechanism of Anomalous Tunneling in Condensed Bose System

We clarify the origin of anomalous tunneling [Yu. Kagan et al. Phys. Rev. Lett. 90 (2003) 130402] i.e. the perfect transmission at low energy limit of tunneling of phonon excitations across the potential barrier separating two Bose condensates. The perfect transmission is a consequence of the coincidence of the wave function of the excited state at low energy limit and the macroscopic wave function of the condensate. We show that the perfect transmission at low energy occurs even at finite temperatures within the scheme of Popov approximation.