Josephson coupling in high-T_c superconducting junctions using ultra-thin BaTiO_3 barriers

摘要

We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa_2Cu_3O_(7-δ) electrodes and a BaTiO_3 barrier with thicknesses between 1 nm and 3 nm. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO_3 barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO_3. The Josephson coupling temperature reduces as the barrier thicknesses increases. The Josephson energies at 12 K are of ≈ 1.5 mV and ≈ 7.5 mV for BaTiO_3 barriers of 1 nm and 2 nm, respectively. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-T_c electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors.