Magnetic Torque Measurements on Bi2201 Single Crystal in High Magnetic Fields

The magnetic field direction dependence of the magnetic torque in the superconducting state of Bi₂Sr_1.65La_0.35CuO_6+δ (Bi2201) single crystal has been measured in several static magnetic fields up to 200 kOe. The applied field dependence of the anisotropy parameter, γ, defined by the square root of the effective mass ratio has been obtained by fitting the magnetic torque curves at 17 K by means of the effective mass model. For Bi₂Sr₂CaCu₂O_8+δ (Bi2212), the γ values up to 210 kOe were reported previously. At each field, γ for Bi2201 is larger than that for Bi2212. Since the γ value decreases as the field increases both for Bi2201 and Bi2212, the reduction of γ by the application of the high magnetic field is considered to be common for Bi-based layered superconductors.