In-Field Transport Properties at Grain Boundaries in BaHfO3-doped SmBa2Cu3Oy Bicrystal Films at Low Temperatures

High-temperature superconducting REBCO tapes are attractive for their high critical current density. Jc in the REBCO film is suppressed under magnetic fields and by grain boundaries. Our group has reported that artificial pinning centers (APC) enhance the Jc 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 Jc 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.