The existence of space inhomogeneous superconductor insulator state (SISIS) found out earlier in polycrystalline samples of high- system ( ？K) is confirmed on single crystal. At ( ？K) the transition from the homogeneous superconducting state into the SISIS occurs. SISIS is characterized by the appearance of two gaps on the Fermi surface, semi- and superconducting, which are modulated in space in antiphase, the electric transport between superconducting regions being carried out due to Josephson tunneling. Thus the whole sample becomes a multiple Josephson system. Nonlinear curves are observed on single crystal at temperatures below . Dependence of curves on temperature and magnetic field, typical to a Josephson system, was found out. Besides, a step-like peculiarity at the values of voltage of the order of one and two superconducting gaps shows up. These peculiarities are suppressed by magnetic field much earlier than critical current. The new data firstly correlate with the model of SISIS and secondly permit for the first time to determining directly the energy gap between homogeneous and stratified superconductor states. 1. Introduction High-temperature superconductor (HTSC) has a cubic lattice and has no copper atoms or any other magnetic ions (has been found out in 1988 [1, 2]). These features distinguish it from other HTSC compounds and do not allow one to justify its HTSC properties on the bases of layered structure or internal magnetic ions. Relative towards high- ？？ is the system [3] famous even before the discovery of high-temperature superconductivity [4] and in behaviour of which different anomalies [5], answering to the spatially inhomogeneous superconductivity, were observed already at the end of the seventies. In subject plan the spectrum of implemented to date researches of high- system appears to be rather wide. Not being exhaustive, the list displayed below illustrates this thematic latitude:(i)problems of synthesis, composition, and structure of high- [6–11];(ii)transport, phonon, and electron-phonon effects [12–14];(iii)heat capacity, thermal expansion, and so forth [15–20];(iv)investigation of magnetic response, accompanying superconducting transition, anisotropy of magnetic properties, and irreversibility effects in remagnetization [21–24];(v)electronic structure and mechanisms of superconductivity [25–36];(vi)superconductivity stratification and phase transitions metal-dielectric [37–40];(vii)Josephson and microwave properties and nonlinear effects under the microwaves action [41–46]. We chose the system for investigation, since,
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