Effect of vortex-vortex interactions on the critical current density of single-crystalline MgB2 thin films

We have investigated the influence of inter-vortex interactions on the critical current density (Jc) and flux pinning properties of single-crystalline MgB2 thin films grown using a hybrid physical-chemical vapor deposition system. Magnetic field dependences of Jc were measured over a 5-35 K range of temperatures for fields applied parallel and perpendicular to the ab-plane of the film's surface. Two regions along the Jc(H) curve, the low-field plateau region and the high-field slope region, which are respectively known as the single-vortex and collective pinning regimes, are clearly distinguishable. A ratio a0/λ between the inter-vortex spacing a0 and the penetration depth λ was calculated at each temperature, to investigate the effect of vortex-vortex interactions on the Jc(H). We found that the a0/λ dependences of the normalized Jc(H,T) data tend to fall onto one curve irrespective of the temperature, if only we use a certain average value of λ. Furthermore, the flux pinning mechanism shows a crossover from δTc-pinning to δl-pinning with increasing magnetic fields, indicating the coexistence of different pinning mechanisms in MgB2.