UPPER CRITICAL-FIELD OF HIGH-T-C OXIDES - EVIDENCE FOR 2E BOSE-LIQUID

We measure and theoretically describe the upper critical field, H-c2(T ), of BSCCO - 2212 crystals with T-c > 92 K by the use of the out-of-p lane resistivity in magnetic fields (H perpendicular to ab) up to 15 T . The empirical procedure is proposed allowing vs to extrapolate the H -c2(T) curve up to H-c2 similar or equal to 230 T and T/T-c similar or equal to 0.35 which is independent of the choice of the R/R(N) ratio. We Sound that H-c2(T) does not follow the conventional theory with or without fluctuations and the magnetic scattering, but is consistent w ith the prediction based on the Bose-Einstein condensation of charged bosons formed above T-c. Our results together with several other measu rements of H-c2 and with the heat capacity data provide an evidence fo r the possibility of 2e Bose liquid ground state of high-T-c oxides.