In-plane anisotropic vortex pinning and relaxation in a stripe-ordered La1.45Nd0.4Sr0.15CuO4 superconductor

The angular dependence of the ac susceptibility for the magnetic field rotated in the CuO2 plane of a stripe-ordered La1.45Nd0.4Sr0.15CuO4 single crystal shows an unusual fourfold symmetry below the superconducting transition temperature (T-c). The real part of the ac susceptibility reaches its maximum for the magnetic field parallel to the stripes, and the in-plane anisotropy of the susceptibility is enhanced with increasing temperature, which indicates that the anisotropy can be ascribed to the vortex pinning of the fourfold symmetric static stripe phase. The in-plane dc magnetic relaxation rate also shows the fourfold symmetry and proves the existence of the anisotropic vortex pinning effect.