Structural origin of enhanced critical temperature in ultrafine multilayers of cuprate superconducting films (original) (raw)

Tuning the Critical Temperature of Cuprate Superconductor Films with

Many of the electronic properties of high-temperature cuprate superconductors (HTSC) are strongly dependent on the number of charge carriers put into the CuO 2 planes (doping). Superconductivity appears over a dome-shaped region of the doping-temperature phase diagram. The highest critical temperature (T c ) is obtained for the so-called "optimum doping". The doping mechanism is usually chemical; it can be done by cationic substitution. This is the case, for example, in La 2Àx Sr x CuO 4 , in which La 3+ is replaced by Sr 2+ , thus adding a hole to the CuO 2 planes. A similar effect is achieved by adding oxygen as in the case of YBa 2 Cu 3 O 6+d (YBCO), where d represents the excess oxygen in the sample. Herein, we report on a different mechanism, one that enables the addition or removal of carriers from the surface of the HTSC. This method utilizes a self-assembled monolayer (SAM) of polar molecules adsorbed on the cuprate surface. In the case of optically active molecules, the polarity of the SAM can be modulated by shining light on the coated surface. This results in light-induced modulation of the superconducting phase transition of the sample. The ability to control the superconducting transition temperature with the use of SAMs makes these surfaces practical for various devices such as switches and detectors based on high-T c superconductors.

Evidence Suggesting Superconductivity at 250 K in a Sequentially Deposited Cuprate Film

Science, 1993

An artificial cuprate compound belonging to the BiSrCaCuO family with eight adjacent CuO, layers in each building block was deposited on a single crystal of SrTiO, by sequentially imposed layer epitaxy. This compound undergoes a five order of magnitude resistivity drop with an onset near 280 kelvin and an offset at 250 kelvin. It exhibits a diamagnetic variation of susceptibility and magnetization below 290 kelvin. Additional observed features, such as strongly nonlinear conductivity, suggests superconductivity as a plausible explanation of the properties of this compound.