Flux pinning and flux creep in La_2-xSr_xCuO₄ with splayed columnar defects

The effects of columnar defects with splayed configurations on flux pinning and flux creep were investigated experimentally. Parallel columnar defects and splayed columnar defects were introduced into specimens of La_2-xSr_xCuO₄ by high-energy heavy-ion irradiation. A large enhancement of the flux pinning and the critical current density J_c due to the splayed columnar defects was observed. At temperature T < 15 K and a magnetic field H = 0.1 T, the effective pinning potential U₀ of a specimen with splayed columns was larger than that of a specimen with parallel columns. On the other hand, at 15 K ≤ T ≤ 30 K and H = 0.1 T, U₀ of a specimen with splayed columns was smaller than that of a specimen with parallel columns.