We have grown a-axis oriented YBa2Cu3O7−y (YBCO) films on LaSrGaO4 (LSGO) (100) substrates with (100) oriented seed layer of PrBa2Cu3O7−x (PBCO) using a pulsed laser deposition technique. PBCO films on LSGO (100) deposited even at ∼800 °C exhibits the a-axis orientation. In this temperature range, PBCO films on SrTiO3 (100) substrate exhibits the c-axis orientation. The YBCO film with a-axis orientation was grown on this PBCO(100) layer at a wide range of 650–800 °C. The YBCO films on PBCO free substrates have, on the other hand, c-axis orientation normal to the surface of the LSGO (100). We found that the preferred orientations of YBCO thin films can be controlled by the presence of PBCO films on LSGO substrate. For the a-axis orientated YBCO films, the resistance perpendicular to the c axis is 1/2 of that parallel to the c axis, suggesting the preferred orientation of c axis along the surface. The zero resistance superconducting transition temperature (Tc) of the films on the LSGO (100) and PBCO (100)/LSGO (100) substrates are 88.0 and 89.0 K, respectively.

YBa2Cu3O7−y (YBCO) microbridges have been fabricated on a SiO2/Si substrate using Y2O3/YSZ (yttria-stabilized zirconia) buffer layer. Using polycrystalline silicon layer overlaid on oxidized Si(100) single crystal, the bridge is microprocessed by means of electron beam lithography and dry etching. The fabricated configuration serves as a mask for depositing YSZ and Y2O3 double buffer layers. The YBCO layer is deposited on the substrate by means of laser ablation deposition. The dimension of the bridge is 1.7 μm wide and 1.3 μm long. The microbridge junctions show a critical temperature of 86 K, and microwave-induced steps are observed indicating the presence of a Josephson junction-type behavior. The IcRn product is 0.5 mV at 30 K.

We report the successful synthesis of insulating LaSrGaO4(LSGO) thin films and YBa2Cu3O7−y(YBCO)/LSGO heteroepitaxial multilayer structures using a pulsed laser deposition technique. SrTiO3(STO)(100) was used as a substrate. The formation of highly c-axis oriented YBCO/LSGO/YBCO trilayer structures is demonstrated. Epitaxial YBCO films on LSGO//STO and LSGO/YBCO//STO have a zero resistance temperature of 88.5 and 88.3 K, respectively. Sandwich-type YBCO/LSGO/YBCO junctions were produced by a suitable patterning technique. The observed (dI/dV)-V characteristics exhibit a clear single gap structure (width ∼26 meV) at temperatures below 30 K.

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Using the pulsed laser deposition technique, we have successfully prepared a-axis oriented PrBa2Cu3−xNbxO7−z (PBCNO)(x=0–1.5) films and YBa2Cu3O7−x (YBCO)/PBCNO heterorepitaxial multilayer structures. For the PBCNO films, the resistivity showed semiconducting behavior at all Nb substitution levels investigated. The resistivity increased with increasing Nb content, reaching a value of 104 Ω cm at 100 K for a 300-Å-thick film with x=1.0. Using (100)SrTiO3 (STO) as a substrate, the following multilayer structures were successfully formed: (100)PBCNO(x=1.0)/(100)YBCO/(100)PBCO//STO, (001) YBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO, and (100)YBCO/(100)PBCO/(100)PBCNO(x=1.0)/(100)PBCO//STO. The bottom and top YBCO layers in the (100)YBCO/(100)PBCO/(100)PBCNO/(100)PBCO/(100)YBCO//STO structure showed superconducting transition temperatures (zero resistance) of 82 and 83 K, respectively. The interlayer resistivity of the 200-Å-thick PBCNO(x=1) interlayer was as high as 105 Ω cm at 30 K.