Tar-Pin Chen

PrBa2[Cu1-xMx]3O7 AS I-LAYER MATERIALS FOR JOSEPHSON SIS JUNCTIONS

Metal (M) doped PrBa2Cu3O7, i.e. PrBa2(Cu1-xMx)3O7 for M=Al, Co, Fe, Ga, Ni and Zn, and x=0.05, 0.10, 0.15, and 0.20 were fabricated. No significant second phase was found for the Al, Co, Fe and Ga doped samples up to 20% doping level. Impurity phases, however, were detected for Ni and Zn doped samples when doping concentration reached 15% and higher. At 77 K the electrical resistivity for most of these compounds is several orders in magnitude higher than that of the PrBa2Cu3O7-δ. Although the lattice parameters in the doped samples changes toward tetragonal structure, all sample remained in orthorhombic structure and the parameters remain very close to those of the undoped one and YBa2Cu3O7-δ. For this reason these compounds may serve as improved I-layer materials for making YBa2Cu3O7-δ SIS Josephson junction.

Electrical transport and Raman spectral studies of (110)-oriented PrBa2 (Cu0.8M0.2)3O7 (M = Ga, Al, Zn, Ni) thin films

The electrical transport and Raman spectral studies of (110)-oriented PrBa2 (Cu0.8M0.2)3O7 (M = Ga, Al, Ni, Zn) (PBCMO) thin films have been investigated. The electrical resistivity, ρ(T), of (110)-oriented PrBa2 (Cu0.8Ga0.2)3O7 (PBCGO) and PrBa2 (Cu0.8Al0.2)3O7 (PBCAO) thin films are many orders of magnitude higher than that of the (110)-oriented PrBa2Cu3O7 (PBCO) thin films and follow Motts 3D variable range hopping law up to room temperature. The electrical resistivity and Raman spectroscopic studies show that Al and Ga ions replace the Cu ions in the Cu-O chains of (110)-oriented PBCO and cause an extensive localization of charge carriers (holes) in the chains site of the PBCO. Our transport studies on YBa2Cu3O7 (YBCO)/PBCGO and YBCO/PBCAO multilayers suggest that PBCAO and PBCGO thin films possess very less or no proximity effects. These results show (110)-oriented PBCGO and PBCAO thin films may serve as very effective insulators in YBCO based superconductor/insulator/superconductor tunneling Joseph...

Electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 thin films

The electrical transport properties of (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 (PBCGO) thin films have been investigated. The electrical resistivity, ρ(T), of (110)-oriented PBCGO thin films is 8.91 × 105 Ω-cm at 77 K, about five orders of magnitude higher than that of the (110)-oriented PrBa2Cu3O7 thin films and follows Mott’s T−1/4 law up to room temperature. Our experimental results suggest filling and localization of holes in Cu-O chains of (110)-oriented PBCGO thin films. We observed very less proximity effect on YBa2Cu3O7 (YBCO)/PBCGO multilayers indicating that the (110)-oriented PBCGO thin films may serve as effective insulators in YBCO SIS tunneling Josephson junction.

Structure and Transport Studies on PrBa2(Cu1-xMx)3O7: M = Al, Fe, and Ni

We have fabricated metal doped PrBa2Cu3O7 (PBCO), i.e. PrBa2(Cu1-xMx)3O7 (PBCMO) with M = Al, Fe, and Ni, and x = 0.05, 0.10, 0.15, and 0.20. X-ray data indicate no significant second phase for Ni-doped samples until 15% doping level is reached. No second phase was found in Al- and Fe-doped samples up to the 20% doping level. All the doped samples are in orthorhombic structure and their lattice parameters are very close to those of YBa2Cu3O7-δ (YBCO). However, for Al or Fe doped samples the difference in lattice parameters a-b has decreased from that of PBCO. At 77 K the electrical resistivity for Al- or Fe-doped samples is several orders in magnitude higher than that of PBCO. Therefore these compounds may be better buffer-layer materials for YBCO superconducting electronic circuits and devices.

TRANSPORT STUDIES ON NANOMETER THICK YBa2Cu3O7-δ MULTILAYERS USING Y0.4Pr0.6Cu3O7 AND PrBa2(Cu0.8Ga0.2)3O7 AS BUFFER LAYERS

We have fabricated PrBa2[Cu1-xGax]3O7 (PBGCO) ceramic samples for x = 0.05, 0.10, 0.15 and 0.20. The electrical resistivities of these samples are many orders of magnitude higher than that of PrBa2Cu3O7 (Pr123) while the other physical properties remain much the same. PBGCO therefore may be a possible buffer layer for YBa2Cu3O7-δ (Y123) superlattices/multilayers. For this reason YBa2Cu3O7-δ/PrBa2(Cu0.8Ga0.2)3O7 (Y123/PBCGO) and YBa2Cu3O7-δ/Y0.4Pr0.6Ba2Cu3O7 (Y123/YPBCO) superlattices were fabricated and their transport properties were studied. It is found that although PBGCO is better for insulating Y123 films in trilayers, inter-Y123 layer coupling exists between separated Y123 layer.

FINITE SIZE EFFECT ON YBCO/PBCAO AND YBCO/PBCGO NANOMETER MULTILAYERS

We have fabricated (110) epitaxy YBa2Cu3O7-δ (YBCO), PrBa2Cu0.8Al0.2O7 (PBCAO), PrBa2Cu0.8Ga0.2O7-δ (PBCGO) nanometer-thin films and YBCO/PBCAO, YBCO/PBCGO multilayers of a variety of film thicknesses. Electrical resistivities measured from these systems were plotted against temperatures and film thicknesses and are presented in this paper. Superconducting onset temperature Tc of the YBCO films was estimated and plotted against YBCO film thickness. Superconducting coupling length was deduced. Finite size effect and 2D to 3D transition are also discussed.