Anisotropy parameter for Bi₂Sr₂CaCu₂O_8+δ single crystal by magnetic torque measurements in high magnetic fields

The applied field dependence of the anisotropy parameter, γ, defined by the square root of the effective mass ratio for the layered superconductor Bi₂Sr₂CaCu₂O_8+δ single crystal has been obtained by the magnetic torque measurements in several static magnetic fields up to 210kOe at 52 and 69 K. Although γ has a huge value of larger than 200 for fields below 20kOe, it becomes less than 60 in 210kOe. It is considered that the huge γ in lower field is affected by the layered structure effect like the intrinsic pinning in addition to the irreversibility due to the flux pinning. The relatively small δ value in higher field reveals the actual effective mass anisotropy.