Magnetization scaling of single-crystal ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$ below ${\mathit{T}}_{\mathit{c}}$

We report magnetization M(H,T) measurements on a superconducting ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ single crystal (${\mathit{T}}_{\mathit{c}}$≃85 K) for H∥c, with 5 K≤T≤90 K and 5 kG≤H≤50 kG. The reversible data show a scaling behavior M(H,T)=m(H)A(T) below ≃70 K and above the irreversibility temperature ${\mathit{T}}_{\mathrm{irr}}$≃30 K. This unexpected result shows that the upper critical field ${\mathit{H}}_{\mathit{c}2}$ is nearly independent of T over this T range, consistent with a T-independent order parameter found recently from other measurements below ≃70 K. Unusual T dependences of the parameters κ and ${\mathit{H}}_{\mathit{c}}$ are also inferred from the data.