On the origin of high-temperature superconductivity in cuprates

Here we review the results of a comprehensive study of high-temperature superconductivity in cuprates that took over ten years to complete. It required development of the technique, for synthesis as well as for measurements of the key physical properties of the superconducting and the normal states, in order to establish their precise dependence on doping, temperature, and external fields. We use atomic-layer-by-layer molecular beam epitaxy to synthesize atomically perfect thin films and multilayers of high-T-c cuprates. We use the mutual inductance technique refined to measure the absolute value of penetration depth lambda to accuracy better than 1%. We have synthesized and studied over 2,000 cuprate films. The large statistics reveals clear trends and intrinsic properties; this is essential when dealing with complex materials such as cuprates. The findings bring in some great surprises, challenge the commonly held beliefs, rule out many models, and point to an unexpected answer to the question why is T-c so high in cuprates.