Microstructures of ramp-edge YBa2Cu3O /PrBa2Cu3O /YBa2Cu3O Josephson junctions on different substrates

Abstract

Ramp-edge YBa2Cu3Ox/PrBa2CuaOx/YBa2Cu30,, Josephson junctions with PrBa2Cu30 . (PrBCO) or SrTiO 3 as a separating layer on different kinds of substrate have been studied by high-resolution electron microscopy. The bottom YBa2CuaO x (YBCO) layer and the separating layer (PrBCO or SrTiO 3) were epitaxially c oriented, irrespective of the substrate (yttria stabilized zirconia (YSZ), SrTiO 3 or NdGaO3, all in (001) orientation). The use of ion milling in the manufacturing of Josephson junctions was found to yield smooth slopes with an angle of about 20 °. The Josephson junction was facing away from the beam direction was found to have a dimple in the substrate near the base of the junction. The barrier layers were observed to have a homogeneous thickness. These layers as well as the top YBCO layers were oriented with their c-axes perpendicular to (001) plane of the substrate for perovskite substrates and perpendicular to the surface for YSZ substrates. In the case of a YSZ substrate, the dimple in the substrate as well as the slope of the substrate close to the base of the junction were found to lead to small-angle grain boundaries in the YBCO film as well as randomly oriented YBCO grains, which results in a poor ramp-edge junction. In the case of SrTiO 3 or NdGaO 3 substrate, all components of the device were fully epitaxial, thus resulting in good ramp-edge junctions.

Interface resistance ofYBa2Cu3O7−δ/La0.67Zalk1, Brinkman2, Aarts3 et al. 2010Phys. Rev. B242141View full textAdd to dashboardCite

“…22,[31][32][33] In transmission electron microscope images, the boundary between the YBCO ramp and the interlayer is indiscernible. 22 Nevertheless, the possibility remains that the material grown on the ramp possesses an increased number of defects, which can lead to bad conductivity.…”

“…10,11 In the normal-state regime, a transition from metallic to insulating behavior was reported for YBCO/ La 0.67 Ca 0. 33 MnO 3 ͑LCMO͒ superlattices, 12 related to a long range charge transfer between the two materials. A similar mechanism was mentioned to explain the observation of suppressed magnetization near this interface.…”

High-Tc ramp-type Josephson junctions on MgO substrates for terahertz applications

“…Microwaves (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) GHz) and millimeter waves (101 GHz) were generated by a synthesized signal generator and a Gunn diode and were fed to ramp-type junctions using a coaxial cable and a waveguide, respectively. Terahertz wave signals were generated by a farinfrared (FIR) laser, pumped by a 38-W CO laser, yielding 40 mW on the 761.7-GHz formic acid line, 100 mW on the 1.40-THz diflorometan line, and 120 mW on the 2.52-THz methanol line.…”

Low- or high-angle Ar ion-beam etching to create ramp-type Josephson junctions

“…The ramp structures they report on were created with perpendicular ion-beam etching. Wen et al [9] report on the microstructure of ramp-type JJs for different substrates. The film deposition and ionbeam etching procedures are largely identical to the one reported here.…”