Upper critical field and anisotropy of the high-${\mathit{T}}_{\mathit{c}}$ ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{\mathit{x}}$ phase

The upper critical field (${\mathit{H}}_{\mathit{c}2}$) of the 110-K ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ phase has been obtained using high-quality whiskers and the measurement of the field-induced resistive transition up to 7.5 T. In the presence of magnetic fields parallel and perpendicular to the c axis, linear relations are obtained in ${\mathit{H}}_{\mathit{c}2}$-T curves defined at the 50% value of the extrapolated normal-state resistivity in the transition curves. According to the Werthamer-Helfand-Hohenberg theory and Ginzburg-Landau relations, the coherence lengths of ${\xi }_{\mathit{a}\mathit{b}}$(0)=29 Å and ${\xi }_{\mathit{c}}$(0)=0.93 Å are obtained. The anisotropy ratio of the coherence length is 31.