| dc.description |
We have measured the temperature dependence of the resistivity ρ of an epitaxial (YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>)<sub>24</sub>/(PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-δ</sub>)<sub>2</sub> multilayer nanometre film at several magnetic fields parallel to the c-axis and at a constant magnetic field H = 4 T. The measurements were taken for various angles α between the magnetic field and the surface of the film with H in the plane between the measuring current I and the c-axis, and for various angles θ between the magnetic field H and the surface of the film (ab-plane) with H ⊥ I. The resistive broadening depends mainly on the effective applied magnetic field H<sub>e</sub> = H×(sin<sup>2</sup>θ + cos<sup>2</sup>θ/γ<sup>2</sup>)<sup>1/2</sup> with respect to the c-axis, and shows a three-dimensional anisotropic behaviour, where γ is the anisotropy parameter. The angular dependences of the peak temperature T<sub>p</sub> and the activation energy U<sub>e</sub> for angle θ and α>5° are in agreement with the effective mass model, namely T<sub>p</sub>(0)-T<sub>p</sub>(H,θ) ∝(sin<sup>2</sup>θ + cos<sup>2</sup>θ/γ<sup>2</sup>)<sup>1/2n</sup> and U<sub>e</sub>∝H<sub>e</sub><sup>-m</sup> with γ = 10, n = 1.31 and m = 0.87. The dissipative resistivity below T<sub>p</sub> for various magnetic fields can be scaled onto a single curve by thermally activated flux motion. When the applied field tilts the CuO<sub>2</sub> plane, the angular dependences of T<sub>p</sub> and U<sub>e</sub> reveal a lock-in transition, showing that the flux lines were trapped in the non-superconducting PrBCO layers. |
