A photodetector with high responsivity has been fabricated with a high quality Y1Ba2Cu3O7−δ film on a regular SrTiO3 (100) substrate that has no thinning or etching. The film exhibits a precipitation-free morphology and has an extremely smooth surface having a rms roughness smaller than 5 nm. The film was patterned into a 25×650 μm2 long microbridge by a conventional photolithography technique. The Tco of the microbridge can be tuned by applying different bias currents, which results in a tunable operation temperature of the photodetector at 77.35±1 K. This makes it operationally more practical and economical. The noise voltage at 10 mA bias current is less than the resolution of our setup, 15 nV  Hz−0.5. A high responsivity of 2.3×103 V/W was obtained when a bias current of 8 mA and a low power density He–Ne laser of 0.08 J/cm2 s chopped at 2 Hz were applied on the microbridge at 77.35 K. Under the same condition, the noise equivalent power (NEP) and detectivity (D*) have been measured to be 4.34×10−12 W Hz−0.5 and 3×109 cm Hz0.5 W−1, respectively.

We report microstructures of superconducting YBa2Cu3O7−x thin films epitaxially grown on a SrTiO3(100) substrate. Transmission electron microscopy studies reveal epitaxial, highly ordered grains ∼5000 Å in size for both types of films with either the a or c axis perpendicular to the film. Defects due to out-of-phase boundaries are observed in the former case. The high density of twin boundaries found in the latter case seems to correlate with the higher Jc observed in thin-film samples.

No abstract

We study the dynamics of a three-dimensional laser bullet propagating inside a nonlinear saturable medium. We show that an increase of the pump parameter destabilizes the bullet and leads to its destruction through oscillations with increasing amplitude. We propose an inhomogeneous and anisotropic external excitation mechanism leading to a stable oscillating bullet. By varying the frequency of the external excitation, a stable quasi-in-phase or quasi-antiphase internal state can be reached.

A new technique using ion beams to produce patterned thin films of the high-temperature perovskite superconductor YBa2Cu3O7−x from spin-on metalorganic precursors is described. Spin-coated precursor films are irradiated through a stencil mask with 2.5 MeV He+ ions, developed in solvent to remove unexposed material, and the remaining patterns are pyrolyzed. Black films of YBa2Cu3O7−x with pattern dimensions on the millimeter scale exhibit orientation with the c axis perpendicular to the film after heat treatments of 990 °C for 3 min. The conductivity of a highly oriented, ∼0.4-μm-thick patterned film is characterized by onset of the superconducting transition at 84 K and zero resistivity at 68 K, similar to those of an unirradiated film given the same thermal treatment. Studies on the nature of the ion beam exposed material are discussed.