Tunneling in all-high-Tc edge junctions with deposited barriers (original) (raw)

1992, Physical review. B, Condensed matter

All-high-T,-material edge junctions consisting of laser-ablated Y-Ba-Cu-0 electrodes and an in situ rf-sputter-deposited MgO barrier have been fabricated whose I-V characteristics show tunneling-related effects. These include a junction resistance with an exponential dependence on the nominal-barrier thickness, gaplike structure observed in the conductance curves, and Josephson effects. These properties are very sensitive to the choice of materials-processsing method for the junction interfaces. Tunneling is a powerful technique for studying the physical properties of superconductors and has also led to many interesting applications. ' Since the advent of high-T, materials, many attempts have been made to study tunneling in these materials both by scanning tunneling microscopy (STM), and by building a variety of tunnel junction structures including point contracts. While most of this work has concentrated on transport from high T, to low T, or to a normal metal, there has been some work on all-high-T, junctions. However, due to the numerous materials problems encountered in high-T, work, it has been difficult to achieve all-high-T, junctions " with some control over the junction characteristics and, in particular, the barrier region. For example, if tunneling is the dominant mode of transport across the barrier, then the resistance of the junctions should depend exponentially on the barrier thickness. In this paper we report on the in situ fabrication of all-high-T, (Y-Ba-Cu-0) edge junctions in which sputter-deposited MgO barriers are used in the thickness range of 0.5-2 nm. In this range the junction resistances are observed to change by about four orders of magnitude. These junctions also exhibit a variety of tunnel-related e8'ects such as gaplike structure in the higher-resistance samples and Josephson e6'ects in the low-resistance samples.