Resistive Upper Critical Field of High- $T_c$ Single Crystals of B${\mathrm{i}}_2$S${\mathrm{r}}_2$CaC${\mathrm{u}}_2$${\mathrm{O}}_8$

The upper critical field $H_{c2\mathrm{}}\left(T\right)$ of B${\mathrm{i}}_2$S${\mathrm{r}}_2$CaC${\mathrm{u}}_2$ ${\mathrm{O}}_8$ crystals with $T_c>92\mathrm{K}$ has been measured from the out-of-plane resistivity in magnetic fields $\left(\mathbf{H}\perp \mathrm{ab}\right)$ up to 15 T. By the use of the empirical procedure the $H_{c2\mathrm{}}\left(T\right)$ curve has been extrapolated up to $H_{c2\mathrm{}}\simeq 230\mathrm{T}$ and ${T/T}_c\simeq 0.35$ which is independent of the choice of the ${R/R}_N$ ratio. We found that $H_{c2\mathrm{}}\left(T\right)$ does not follow the conventional theory with or without fluctuations but is consistent with the prediction based on the Bose-Einstein condensation of charged bosons formed above $T_c$. Our results together with the heat capacity measurements provide an evidence for the possibility of $2e$ Bose liquid ground state of $\mathrm{h}\mathrm{i}\mathrm{g}\mathrm{h}-T_c$ oxides.