Josephson coupling in high-T${}_c$ superconducting junctions using ultra-thin BaTiO${}_3$ barriers

Abstract

We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa${}_2$Cu${}_3$O${}_{7-d}$ electrodes and a BaTiO${}_3$ barrier with thicknesses between 1 nm and 3 nm. The junctions with an area of 20 mm x 20 mm were fabricated combining optical lithography and ion etching using GdBa${}_2$Cu${}_3$O${}_{7-d}$ (16 nm) / BaTiO${}_3$ (1 - 3 nm) / GdBa${}_2$Cu${}_3$O${}_{7-d}$ (16 nm) trilayers growth by sputtering on (100) SrTiO${}_3$. 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 is strongly reduced for increasing barrier thicknesses, which may be related to the suppression of the superconducting critical temperature in the bottom GdBa${}_2$Cu${}_3$O${}_{7-d}$ due to stress. The Josephson energies at 12 K are of $\approx$ 1.5 mV and $\approx$ 7.5 mV for BaTiO${}_3$ barriers of 1 nm and 2 nm. 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.

References in corpus (1)

• Theoretical current-voltage characteristics of ferroelectric tunnel junctions