B. Oh

Critical current densities and transport in superconducting YBa2Cu3O7−δ films made by electron beam coevaporation

Thin films of the high Tc superconductor YBa2Cu3O7−δ were prepared and characterized. The films made on SrTiO3 showed epitaxial growth and high critical current densities in excess of 9×104 at 78 K and 2×106 at 4.2 K. Also, surface pinning in the parallel direction was found to be very high. The measurements put a lower limit on the depairing critical current density of 5×107 A/cm2.

Thin-film synthesis of the high- T c oxide superconductor YBa 2 Cu 3 O 7 by electron-beam codeposition

The successful synthesis of high- T c YBa 2 Cu 3 O 7 films by means of electron-beam codeposition are reported. Several important growth parameters have been surveyed in a preliminary way. The substrates investigated include Al 2 O 3 , ZrO 2 , MgO, and SrTiO 3 , The films were characterized by resistivity measurements, x-ray diffraction, microprobe, and Rutherford backscattering analysis. Some TEM and critical current density studies were also carried out. The best results to date have been obtained on SrTiO 3 substrates with which polycrystalline epitaxial growth has been achieved. Resistive superconducting transitions with zero resistance at 89.5 K and a 2 K width have been observed in these films.

Scanning tunneling microscopy of the a-b planes of Bi2(Ca,Sr)3Cu2O8+δ single crystal and thin film

A scanning tunneling microscope was used to image the a‐b plane of a single crystal of Bi2(Ca,Sr)3Cu2O8+δ (Tc∼85 K) and a thin film grown epitaxially on a (100) SrTiO3 substrate. Images taken at room temperature in air of a freshly cleaved bulk sample clearly show the one‐dimensional superstructure (27.2±0.7 A periodicity) which is common to this phase. Several images show steps 16 A high, suggesting that the cleavage occurs between 2122 molecular units. The registry of the superstructure from terrace to terrace is either shifted by half a superlattice parameter or is aligned. Images of evaporated thin films show features of comparable size, but not the same long‐range order as the crystal. Low‐temperature conductance measurements of the thin film exhibit a BCS‐like energy gap with 2Δ/kTc≊12.

Two‐dimensional superstructure in the (001) plane of Bi2[Ca,Sr]3Cu2O8+δ thin films

Thin films of Bi‐Ca‐Sr‐Cu‐O showing superconductivity above 100 K have been made by electron beam evaporation with oxygen post‐annealing. The major superconducting phase, Bi2[Ca,Sr]3Cu2O8+δ (Tc ∼85 K), is oriented epitaxially with the (100)SrTiO3 substrate. In addition to the one‐dimensional incommensurate superstructure along the b axis, which is characteristic of this phase, we have observed by transmission electron microscopy a two‐dimensional incommensurate superstructure in the a‐b plane with a different periodicity and a different orientation relationship to the subcell.

Synthesis and properties of superconducting lanthanum sulfide films

Abstract We report the structural and transport properties of La-S films prepared by reactive planar magnetron sputtering. The La-S (Th 3 P 4 cubic structure) can be prepared over a range of compositions with the electronic properties varying from a low electron density superconductor ( T c ≈ 7 K ) to a semiconductor which shows thermally activated transport at low temperature. This method of deposition produces small grained (≈ 200 A) polycrystalline films whose composition can be varied continuously by tuning the deposition parameters. We discuss the TEM and X-ray data as well as the resistivity, Hall effect and superconducting properties of these films. We find that the superconducting transition temperature of the films is the same as that of bulk single crystals; however the mobility is a factor of 2 to 300 lower than that found in bulk specimens.