Angular dependence of resistivity in the superconducting state of NdFeAsO0.82F0.18 single crystals

We report the results of angle dependent resistivity of NdFeAsO0.82F0.18 single crystals in the superconducting state. By doing the scaling of resistivity within the frame of the anisotropic Ginzburg-Landau theory, it is found that the angle dependent resistivity measured under different magnetic fields at a certain temperature can be collapsed onto one curve. As a scaling parameter, the anisotropy Gamma can be determined for different temperatures. It is found that Gamma(T) increases slowly with decreasing temperature, varying from Gamma similar or equal to 5.48 at T = 50 K to Gamma similar or equal to 6.24 at T = 44 K. This temperature dependence can be understood within the picture of multi-band superconductivity.