Dissipative quantum-creep studies in single-crystal La2CuO4+δ

Temperature-dependent magnetic relaxation was studied in a La₂CuO_4+δ crystal in the low-temperature range 2–10 K. The experimental data exhibited a non-vanishing magnetic relaxation in the low-temperature limit. These data could be well interpreted by a quantum-creep theory, suggesting the non-vanishing relaxation at low temperatures due to quantum tunneling of vortices. The effective Euclidean action determined as /|d ln M/d ln t| showed a quadratic temperature dependence. The quantitative analysis of the effective Euclidean action yields a classical activation energy, crossover temperature and zero-temperature quantum-tunneling rate.