(BaCuO2+δ)m/(CaCuO2)2 superconducting artificial structures were synthesized by layer by layer pulsed laser deposition. The interlayer coupling between adjacent superconducting CaCuO2 blocks was investigated. The thickness of the BaCuO2+δ charge reservoir (CR) layer was gradually increased up to m=10. It was found that interlayer coupling is not essential for high Tc superconductivity: giant CR blocks, thicker than 20 angstrom, (m ≈ 5), depress only moderately Tc while increase the 2D character of superconductivity. Furthermore hetero-epitaxial (BaCuO2+δ)m/(CaCuO2)2/(BaCuO2+δ)m tri-layers made of a single superconducting block sandwiched between two CR blocks were deposited. Electrical transport measurements showed that such ultra thin structures are superconducting with Tc up to about 60 K and critical current densities (at 4 K) as high as 108 A cm-2. Such finding confirmed the occurrence of purely intralayer superconductivity in these artificial structures.
In this paper we show that (BaCuO2)m/((Ca,Sr)CuO2)n superlattices with good crystallographic quality can be engineered by Pulsed Laser Deposition in a wide range of composition, namely for m equals 2 and n ranging form 1 to 6. The temperature dependence of resistivity of the superlattices grown at relatively high oxygen pressure and temperatures above 570 degrees C is metallic with a full transition to a superconductive state. For optimized growth conditions, the critical temperature can reach a value of about 80 K. We investigated some of the electrical transport properties of these superlattices. The result of these measurements indicate, for these artificial structures, an intermediate degree of anisotropy between the highly anisotropic BSCCO and the relatively isotropic YBCO. Moreover, the dependence of Tc on the number of CaCuO2 layers was investigated and a maximum was found for n equals 2-3.
Pulsed laser deposition technique (PLD) has been successfully used to grow artificially layered films of the CuBa2(Ca1-xSrx)n-1 CunOy compound using only two targets having nominal composition BaCuOy and (Ca1-xSrx)CuOy respectively. n was varied between 2 and 5. The kinematic analysis of the x-ray diffraction spectra reveals that the average random discrete thickness fluctuations which affects both the BaCuOy and (Ca1-xSrx)CuOy layers are much smaller than one atomic layer. Such features are confirmed by the appearance of sharp peaks even for the nequals2 artificially layered structure where only one (Ca1-xSrx)CuOy cell is deposited in the stacking sequence. A major difference is found in the behavior of resistivity between films containing Sr and Ca respectively. Namely (BaCuO2)2/[(Ca1-xSrx)CuOy]n films never show any trace of superconductivity, while [BaCuO2]n/[CaCuO2]n films result to have, for growth oxygen pressures P > 0.2 mbar a full transition by laser deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high Tc structures by the PLD technique.
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