In-Field Transport Properties at Grain Boundaries in BaHfO 3 -doped SmBa 2 Cu 3 O y Bicrystal Films at Low Temperatures

High-temperature superconducting REBCO tapes are attractive for their high critical current density. J c in the REBCO film is suppressed under magnetic fields and by grain boundaries. Our group has reported that artificial pinning centers (APC) enhance the J c at the grain boundaries in the REBCO films at the liquid nitrogen temperature of 77 K. In this study, we have extended our previous work to a lower temperature since the usage of the REBCO tapes at a lower temperature and a high magnetic field is a recent development trend. Transport characteristics at grain boundaries in the REBCO films with and without APC are investigated at temperatures down to 4.2 K and at magnetic fields up to 9 T. The results show that the introduction of the APCs is effective to enhance the J c at the grain boundaries at low temperatures and at the magnetic fields, especially around the matching field where the density of the APC is equal to that of vortices.