We report the synthesis of superconducting MgB2 thin films grown in situ by molecular-beam epitaxy. Mg-rich fluxes are deposited with B flux by electron-beam evaporation onto c-plane sapphire substrates. The films exhibit c-axis oriented peaks of MgB2, and a full width at half maximum of 3° in their rocking curves. In-plane alignment of MgB2 shows 12-fold symmetry, which is observed by the selected area diffraction pattern in transmission electron microscopy. The MgB2 films show a superconducting transition at 34.5 K with ΔTc<1 K. Even though the residual resistivity of the films is quite high (∼60 μΩ cm), the normal-state resistivity has a very similar temperature dependence but is five times larger than that of a single crystal, implying that conduction through the whole sample is imperfectly connected or inhomogeneous. Upper critical fields are obtained from measurement of the field dependence of the resistivity. It is estimated that the upper critical field at 20 K is more than 15 T, which is one of the largest values ever reported.

High-rate (10 nm/s) in situ YBa2Cu3O7 (YBCO) film growth was demonstrated by molecular beam epitaxy with electron beam co-evaporation at a system pressure of approximately 5 × 10-5 Torr. To explain the phase stability observed, it is suggested that activated oxygen is generated in the process. Growth of very good YBCO, with a Jc of more than 2 MA/cm2, is possible at this very high rate because the growth is in a liquid (Ba–Cu–O), which forms along with the YBCO epitaxy. This liquid seems essential for high Jc-YBCO film growth at very high in situ growth rates and may be essential for all high-rate processes, including postanneal ex situ processes.

We have fabricated and tested two-dimensional arrays of YBa2Cu3O7−δ superconducting quantum interference devices. The arrays contain over 36 000 nano Josephson junctions fabricated from ion irradiation of YBa2Cu3O7−δ through narrow slits in a resist-mask that was patterned with electron beam lithography and reactive ion etching. Measurements of current-biased arrays in magnetic field exhibit large voltage modulations as high as 30 mV.

This paper presents a simple and effective approach to increase the normal zone propagation velocity (NZPV) in (RE)BaCuO thin films grown on a flexible metallic substrate. The concept is an extension of the current-flow-diverter concept already known in the literature. The key idea behind the novel approach is to use a specific geometry of the silver thermal stabilizer that surrounds the superconducting tape. More specifically, a very thin layer of silver stabilizer is deposited on top of the superconductor layer, typically less than 100nm, while the remaining stabilizer (still silver) is deposited on the substrate side. Normal zone propagation velocities up to 170cm s −1 at 77K have been measured experimentally for the first time with this novel architecture, corresponding to a stabilizer thickness of 20nm on top of the superconductor layer. This is at least one order of magnitude faster than the NZPV speeds measured on commercial 2G HTS tapes. Our results clearly demonstrate that a very thin stabilizer on top of the superconductor layer leads to high normal zone propagation velocities. The experimental values are in good agreement with predictions realized by finite element simulations. Furthermore, the propagation of the normal zone during the quench was recorded in situ and in real time using a high-speed camera. Due to high Joule losses generated on both edges of the tape sample, a 'Ushaped' profile could be observed at the boundaries between the superconducting and the normal zones, which matches very closely the profiles predicted by the simulations. The most direct application of this new HTS tape architecture is in high field magnets, since faster quench propagation allows easier detection and protection, which is likely to accelerate substantially the development of HTS magnets used as high-field MRI/NMR systems, etc.

We report the synthesis of superconducting MgB2 thin films grown in-situ by molecular beam epitaxy (MBE). Mg-rich fluxes are deposited with B-flux by electron beam evaporation onto c- and r-plane sapphire substrates. Deposition temperature is varied between 260 ∼ 320 °C. Base pressure of the MBE chamber is at low 10-10 Torr, rising to 10-8 Torr during deposition due mostly to the presence of hydrogen and nitrogen. Asgrown MgB2 films show superconducting transition at ∼ 34 K with ΔTc < 1 K. The films on c-plane sapphire substrates exhibit c-axis oriented peaks of MgB2, and full-width at half maximum of 3 degree in their rocking curves. Azimuthal phi-scan of the MgB2(101) peak shows 12-fold symmetric peaks, which is confirmed by selected area diffraction pattern in transmission electron microscopy (TEM). Plan-view TEM shows hexagonal-shaped grain growth with grain size of about 400 Å.