DEPOSITION OF (Ba, La)CuO₂/CaCuO₂ SUPERCONDUCTING MULTILAYERS BY PULSED LASER ABLATION

Abstract

Superconducting multilayers, whose growth and structure are determined by the kinetic deposition instead by thermodynamics, are a powerful tool for investigating high T c superconductors (HTSC) properties. By means of Pulsed Laser Deposition (PLD), we grew such materials alternating infinite layer phases both pure and doped, to supply Cu0 2 planes and charge reservoir (CR) blocks respectively. We found out that using chemically doped CR leads to a semiconducting behavior, whereas oxygen doping seems to be much more effective, since the BaCu0 2 infinite phase, grown in high oxygen partial pressure, does actually bring about a superconducting behavior. We deposited BaCu0 2 /CaCu0 2 superlattices with various periodicities and studied their transport and structural properties. By varying the deposition parameters, we reached both kinetic and thermodynamic growth and we observed semiconducting and superconducting behaviors.

Transport property characterization of (Ba, La)CuO2/CaCuO2superconducting multilayers deposited by pulsed laser ablation

“…The different growth mechanisms and the various obtainable phases can be described by varying the deposition temperature between 500 and 650 • C while keeping the oxygen pressure as high as 1 mbar, in order to introduce as much excess oxygen as possible in the BL. At low temperatures, between 500 and 530 • C, structurally good superlattices with different periodicities can be obtained [4,10,11]. These samples, in spite of their low resistivity value (less than 10 m cm [11]) at room temperature, exhibit a semiconducting behaviour; although they are not far from the metal-insulator transition, the charge introduced is still too low for any oxygen pressure value.…”

“…At low temperatures, between 500 and 530 • C, structurally good superlattices with different periodicities can be obtained [4,10,11]. These samples, in spite of their low resistivity value (less than 10 m cm [11]) at room temperature, exhibit a semiconducting behaviour; although they are not far from the metal-insulator transition, the charge introduced is still too low for any oxygen pressure value.…”

“…(BaCuO 2+δ ) 2 /(CaCuO 2 ) n superconducting superlattices have been grown for different values of n with critical temperatures up to 80 K [4,9]; as we will explain in the following, these phases, that are in any case very unstable in time, can lead to a superconducting behaviour only in a very narrow range of deposition conditions. In previous works [10,11] we suggested substituting trivalent La ions on Ba sites in order to stabilize the phase.…”