****Technical Abstract**** The project is concerned with high-temperature superconducting pairing in nanoclusters composed of tens to hundreds of atoms in size. The distinct character of their electronic states - "shell structure" ordering - makes such clusters especially promising nanoscale systems for this research. Particles of specific sizes are anticipated to display pairing that is greatly enhanced relative to bulk samples, with a concomitant increase in the critical temperature. The implication is a path towards superconductivity at unprecedented temperatures of 200 K or higher, possibly at room temperature. In the first stage of the project, the influence of pairing on the electronic spectrum will be pinpointed in free clusters by a measurement of photoionization thresholds as a function of temperature and size. In the second stage, prototype circuits will be produced by soft-landing size-selected nanoclusters on suspended nanotubes. The deposited clusters will form a discrete chain along the nanotube, and the nanotube's conductivity will be modified by the proximity effect. This approach combines high sensitivity to individual nanoparticles with the ability to tune their parameters. The ultimate goal is to merge an orders-of-magnitude increase in superconducting current capacity with an orders-of-magnitude increase in the operating temperature, leading to advances in, and applications of, nanoscale superconducting transport. The project offers students and postdocs excellent training in a wide range of experimental and theoretical aspects of an inherently interdisciplinary field.
The phenomenon of superconductivity, discovered 100 years ago, is one of the most fascinating, complex, useful and important effects in physics. Some materials completely lose their electrical resistance when cooled below their "critical temperature." For many decades it appeared that critical temperatures may be limited to very low values, close to the absolute zero. Thus applications were valuable (e.g., medical MRI, particle accelerators) but expensive and limited. In the last twenty years the field has blossomed, as scientists realized that superconductivity "lurks" in many more materials and at higher temperatures. An aspiration is to discover systems with still higher critical temperatures, desirably even at room temperature. This project will advance this goal by combining the pursuit of high-temperature superconductivity with the realm of nanoscience, by detecting the superconducting transition in nanoclusters. Nanoclusters are aggregates of a finite number of metal atoms, from tens to hundreds, and can be precisely size-selected. It is anticipated that nanoclusters of certain sizes will display superconductivity at temperatures of 200 Kelvin or even higher, possibly reaching room temperature levels. Furthermore, circuits built out of such nanoclusters can transmit high currents without resistance. The graduate and undergraduate students and postdocs participating in the project will receive training in a wide range of skills associated with this interdisciplinary field of science. The subject matter is also fruitful for outreach programs for undergraduate, elementary-school, and high-school students.
