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ABSTRACT: We report the use of an epitaxial barrier of Y <sub> 0.8 </sub> Pr <sub> 0.2 </sub> Ba <sub> 2 </sub> Cu <sub> 2.7 </sub> Co <sub> 0.3 </sub> O <sub> 7-δ </sub> in order to study the effect of Pr in the barrier layer. The bulk behavior of this Pr and Co-doped YBa <sub> 2 </sub> Cu <sub> 3 </sub> O <sub> 7-δ </sub> (YBCO) material shows it is just on the insulating side of the metal–insulator transition. We present the temperature dependence of the critical current I<sub>c</sub> and the resistance R<sub>n</sub> for junctions with 150-, 300-, and 450-Å-thick barriers of Y <sub> 0.8 </sub> Pr <sub> 0.2 </sub> Ba <sub> 2 </sub> Cu <sub> 2.7 </sub> Co <sub> 0.3 </sub> O <sub> 7-δ </sub>. The temperature dependence of the critical currents was analyzed within the framework of the proximity effect of de Gennes. The fittings show that the junctions are in the dirty limit with a diffusion constant of D=2.3 cm <sup> 2 </sup> /s and a pair-breaking scattering time of 8.6×10<sup>-14</sup> s . The value of the diffusion constant is three times lower than the value we have found in the pure 14% Co-doped YBCO barrier, showing that the Pr doping decreases the mean free path in the junction barrier. The presence of the inelastic pair-breaking process was identified as a key issue in the barrier near the metal–insulator transition. © 1997 Ameri-
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can Institute of Physics.
Applied Physics Letters 07/1997; · 3.84 Impact Factor
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ABSTRACT: A scanning probe microscope was used to induce local, nonvolatile field effects in epitaxial, ferroelectric Pb(Zr0.52Ti0.48)O3/SrRuO3heterostructures. Field-effected regions with linewidths as small as 3500 angstroms were written by locally switching the
polarization field of the Pb(Zr0.52Ti0.48)O3layer; the electronic density of the underlying metallic SrRuO3 layer was modified and the sheet resistance was changed by up to 300 ohms per square. This procedure is completely reversible
and allows submicrometer electronic features to be written directly in two dimensions, with no external electrical contacts
or lithographic steps required.
Science 05/1997; 276(5315):1100-1103. · 31.20 Impact Factor
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ABSTRACT: We report on the growth and properties of (Sr <sub>1-x</sub> Ca <sub>x</sub>) RuO <sub> 3 </sub> and Sr (Ru <sub>1-x</sub> Ti <sub>x</sub>) O <sub> 3 </sub> thin films obtained by sequential deposition of submonolayers from end members of each compound. Magnetization measurements as well as transport properties exhibit a very different behavior for each type of substitution. A simple model, which assumes a random distribution of the substituted sites, allows us to account quantitatively for the reduction of the magnetization with increased doping and further confirms the homogeneity of our samples. A strong distortion due to the presence of the Ti on the Ru site could explain the different behavior observed between both types of doping. © 1997 American Institute of Physics.
Applied Physics Letters 02/1997; · 3.84 Impact Factor
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ABSTRACT: We report the observation of a ferroelectric field effect in the conducting oxide SrRuO3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Upon reversing the polarization of the ferroelectric Pb(Zr0.52Ti0.48)O3 layer, we measured a 9% change in the resistance of a nominally 30 Å SrRuO3 film at room temperature. This change was nonvolatile for a period of several days. Conductivity measurements taken between 4.2 and 300 K are consistent with n-type conduction throughout this temperature range. Hall effect measurements also yield n-type conduction, with n ≈ 2×1022 electrons/cm3, and furthermore allow us to understand quantitatively the magnitude of the observed resistivity change. © 1997 American Institute of Physics.
Applied Physics Letters 01/1997; 70(2):206-208. · 3.84 Impact Factor
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ABSTRACT: Using scanning probe microscopy, we have written nonvolatile electronic nanofeatures in the metallic perovskite oxide SrRuO3. The structures were written in epitaxial thin film Pb(Zr0.52Ti0.48)O3 (PZT) / SrRuO3 heterostructures by locally switching the polarization field of the ferroelectric PZT layer with an atomic force microscope (AFM). The resulting field effect changes the sheet resistance of the SrRuO3 layer by up to 300 ohms per square. Using the AFM as an electric field microscope, it is also possible to visualize the charge distribution of the written areas on the PZT surface. Large areas of up to 100 μm2 have been polarized and imaged with submicrometer resolution, with the smallest features having linewidths of 170 nm. This approach to local electronic doping is reversible and allows one to write nonvolatile submicron electronic features in two dimensions without lithographic steps or permanent electrical contacts required.
MRS Proceedings. 12/1996; 493.
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ABSTRACT: We present the conductance–voltage characteristics of interfaces between YBa2Cu3O7 and three conductive metallic oxides; CaRuO3, SrRuO3, and La0.5Sr0.5CoO3. In the case of all the YBa2Cu3O7/(Ca,Sr)RuO3 interfaces, we observe the zero bias conductance peaks with the increasing conductance background at high bias. The zero bias conductance peaks decrease with increasing temperature and disappear at temperatures between 30 and 40 K. However, we did not observe zero bias anomalies in the YBCO/La0.5Sr0.5CoO3 contacts, in spite of an interface resistance of similar magnitude. This work suggests that the origin of the zero bias conductance peak lies in the defects on the YBCO surface and the exact defect structure depends on the adjacent epitaxial material. © 1996 American Institute of Physics.
Applied Physics Letters 02/1996; 68(7):1009-1011. · 3.84 Impact Factor
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ABSTRACT: We report on ferroelectric field effect experiments on Pb(Zr0.52Ti0.48)O3/SrCuO2 and Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures with an emphasis on the material characterization. Upon reversing the polarization of the Pb(Zr0.52Ti0.48)O3 ferroelectric layer, we measured a nonvolatile change in the resistivity of ultrathin layers of SrCuO2 and SrRuO3. In thin SrRuO3 films (30 ) up to a 9% resistivity change has been observed at room temperature.
Journal of Low Temperature Physics 01/1996; 105(5):1517-1522. · 1.19 Impact Factor
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ABSTRACT: The low frequency current–voltage characteristics of YBa 2 Cu 3 O 7 –SrRuO 3 –YBa 2 Cu 3 O 7 Josephson junctions show an increasing resistance and phase shift in fields of 0 to 8 T. A critical current is also evident up to 8 T. Data are analyzed in terms of field‐induced perturbations of the current paths through the junction. Results indicate a highly inhomogeneous interface where the mean width of spatial variations in both normal and supercurrent is of order 50 to 100 Å. © 1995 American Institute of Physics.
Applied Physics Letters 09/1995; · 3.84 Impact Factor
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ABSTRACT: We report the properties of YBa 2 Cu 3 O 7-x /YBa 2 Cu 2.79 Co 0.21 O 7-x /YBa 2 Cu 3 O 7-x junctions in an edge junction geometry as a function of temperature and barrier thickness. The barrier material used in this work, YBa 2 Cu 2.79 Co 0.21 O 7-x , is an underdoped version of YBa 2 Cu 3 O 7-x , which has a lower carrier density, a lower T c , and a higher anisotropy than YBa 2 Cu 3 O 7-x . The resistances of the junctions are proportional to the thicknesses of their barriers, suggesting the presence of very little interface resistance. The temperature dependences of critical currents and junction resistances show behavior consistent with that predicted by the conventional proximity effect.
Applied Physics Letters 09/1994; · 3.84 Impact Factor
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ABSTRACT: We have measured interface resistances in YBa 2 Cu 3 O 7-x /barrier/YBa 2 Cu 3 O 7-x junctions with different barrier materials in an edge junction geometry. CaRuO 3 , La 0.5 Sr 0.5 CoO 3 , Y 0.7 Ca 0.3 Ba 2 Cu 3 O 7-x , YBa 2 Cu 2.79 Co 0.21 O 7-x , and La 1.4 Sr 0.6 CuO 4 have been employed as the epitaxial barrier materials. We observe interface resistances of the order of 1×10<sup>-8</sup> Ω cm<sup>2</sup> when we use CaRuO 3 and La 0.5 Sr 0.5 CoO 3 barriers. These two barrier materials are cubic perovskites. However, in the case of the layered barrier materials, the measured interface resistances are smaller than 1×10<sup>-10</sup> Ω cm<sup>2</sup>. Our study suggests that the oxygen disorder at the YBa 2 Cu 3 O 7-x surface, due to stress created by the thermal expansion mismatch between YBa 2 Cu 3 O 7-x and the barrier, may be the origin of the interface resistances, and that the magnitude of this stress can change the resistance by orders of magnitude.
Applied Physics Letters 11/1993; · 3.84 Impact Factor
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ABSTRACT: Epitaxial barriers of ferromagnetic SrRuO 3 have been used to fabricate high T c superconductor‐normal‐superconductor Josephson junctions in the edge junction geometry. At small barrier thicknesses the SrRuO 3 junctions follow the behavior of nonferromagnetic but otherwise closely related CaRuO 3 junctions. A rapid disappearance of critical current is observed when the barrier thickness is increased to 250 Å. Possible origins of such a large critical thickness are discussed.
Applied Physics Letters 09/1993; · 3.84 Impact Factor
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