This letter describes the scaling behavior and Josephson properties of improved YBCO/PBCO/ YBCO edge-type junctions. The critical current, normal-state resistance, and I& product scale with barrier thickness and junction area. The coherence length of the PBCO barrier is estimated to be between 5 and 8 nm. As unambiguous evidence of the Josephson behavior, the microwave response as a function of microwave power, as well as the current modulation with applied magnetic field, have been studied: well-developed Shapiro steps at 10 GHz have been observed, and the modulation of I,(H) shows Fraunhoferlike behavior with 95% Ic suppression.We have previously reported the fabrication of highquality epitaxial, all high-l', edge-type YBa&!usO, (YBCO)/PrBa&!u~O,(PBCO)/YBCO Josephson junctions,"' prepared with our modified off-axis sputtering technique.3s4 These junctions have shown Josephson behavior up to rather high temperatures, and dc SQUIDS with such junctions are promising for practical applications. However, the physical properties of these junctions are far from clear. For fabrication of really controllable and uniform junctions, these properties must be studied. The scaling behavior, intrinsic parameters, and magnetic field modulation, as well as the microwave response of our edge junctions, are presented here. the intrinsic nature of the PBCO might play a role.Our junctions show good uniformity in the scaling of the critical current and the inverse normal resistance with the junction area, defined as A = wXd/sin i) (w is the junction width, d is the thickness of the base electrode, and 6 is the angle of the junction edge). This is shown in Fig. 1 for junctions with the same barrier thickness. The values for the smallest junctions may be somewhat too low due to the larger influence of the damaged edge by ion etching. At any rate, Fig. 1 demonstrates uniform behavior with different junction areas.The dependence of J, on the-R;Rk product has -been investigated as well. The data shown in Fig. 3 are distributed along the line J,-(R&) -m, with m = 1.2. For SNS structures with L&, one would expect J,-(Rd) -2, whereas for superconductor/insulator/normal-metal/ superconductor (SINS) structures J,-(R&) -' (Refs. 5 and 6). The observed dependence differs from the predjction for SNS structures and more closely resembles that for SINS structures. On the other hand, the temperature dependence of the critical-current density,.-( 1 -T/T,)', is in good agreement with the SNS type model, as we reported earlier.' This discrepancy may 'be attributed to the interface resistance between the base elcctrode and PBCO barrier, and the influence of the speci:iic resistance of PBCO, which may be different for Lscn or Lci5rIn addition, the I,$, products have been found to scale nearly linearly with L, ranging from 0.8 to 5 mV. TG highest values obtained were 8 mV. The damage of the edge surface due to our ex situ process could also detri-A strong dependence of the critical current density J, on the PBCO barrier thickness L has been observed....

A detailed study of the fabrication process, current voltage (I-V) characteristics, and Josephson and normal-state properties of the YBa2Cu3Ox(YBCO)/PrBa2Cu3Ox(PBCO)/YBCO ramp junctions is presented. The I-V characteristics can be well described by the resistively shunted junction model. It was found that the critical current Ic and the normal-state conductance 1/Rn scale linearly with the junction area, whereas Ic, the excess current Iex, and IcRn products decrease with increasing barrier thickness. These junctions with cross-sectional area A have a good controllability, low capacitance, and high values of IcRn and RnA products. The coherence length ξn of the PBCO barrier is estimated to be between 5 and 8 nm. As unambiguous evidence of the Josephson behavior, the microwave response as a function of the microwave power as well as the modulations of critical current Ic(H) with applied magnetic field are shown. A modulation depth of more than 95% has been observed. Small proximity effect parameters and junction capacitance (C/A∼10−7 F/cm2) show an advantage of these junctions for many applications.

A study of the YBCO/PBCO/YBCO ramp junctions with and without PBCO barrier shows that the Josephson and normal state behavior of these structures are determined by the thickness of the PBCO barrier and its nature. The boundary resistance and depression of the YBCO superconducting parameters near the interface do not strongly affect the junction characteristic. For thicknesses of 8 to 20 nm of the PBCO barrier the Josephson coupling is established through the high resistive barrier and the behavior of the junctions is better described by a SNINS model than by a SNS weak link model. Proximity effect, resonant tunneling and strong pair breaking mechanisms are discussed to explain the experimental characteristics. Good agreement with the experimental dependence of the IcR, product on the temperature and on the PBCO barrier thickness was obtained ifa strong pair breaking mechanisms in the barrier is taken into account.

Abstra&Electricfield effect devices and quasiparticle injection effect devices are good candidates for the realization of three terminal devices from high-T, materials, since they take explicit advantage of the low carrier concentration in these compounds. We describe the fabrication and operation of both types of devices, and discuss their performance as transistor-like elements.

The behaviour of t h e crystal structure of the YBCO epitaxial films with enlarged c-axis parameter has been studied. The c-axis expansion effect is shown to be induced by low oxygen partial pressure during the film deposition. This effect cannot be explained only by oxTgen deficit in the C u 4 chains or (Y. Ea) cation disorder. A bridging oxygen disorder model shows qualitative agreement with experimental x-ray diffraction spectra. Thermodynamic analysis of the formation of oxygen vacancies shows the high theoretical density of the bridging oxygen vacancies at the film synthesis temperatures.