Imaging the Gauge-Invariant Phase Difference of Superconductors

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Non-Technical:This project will construct a novel type of scanning tunneling microscope and use it to study superconductors at the atomic scale at temperatures that are a small fraction of a degree above absolute zero. The microscope includes a sharply pointed tip, which can be moved in a controlled manner across a surface under study, and the associated electronics for measuring the electric current that flows between the tip and the surface. Changes in this current (the tunneling current) as the tip is moved over the surface indicate variations in the properties of this surface. The goal of the project is not only to develop a new type of imaging but also to obtain insight into the as yet unknown mechanism that is producing high-temperature superconductivity. Knowledge of this mechanism could lead to new superconductors with transition temperatures that are high enough to have a significant impact on technology. Other broad impacts include training of graduate students and postdoctoral students in areas of continuing scientific and technological importance, including low-temperature physics, microscopy at the atomic scale, materials physics, and superconductivity. The project will work to increase the participation of women and minorities in the physical sciences, improve undergraduate and graduate education in physics, and foster collaborations with scientists from Latin America and Eastern Europe.Technical:This project will build a novel type of low temperature scanning tunneling microscope (STM) and use it to measure spatial variations in the phase difference of superconductors at the atomic scale. This microscope consists of a Josephson junction connected in parallel with a vacuum tunnel junction, which is formed between the superconducting STM tip and the surface of the superconductor under study. To minimize the impact of thermally generated noise, the entire system will be cooled in a dilution refrigerator to below 0.1 K. After testing on a well-understood superconducting material, the system will be used to examine spatial variations in the local phase difference near atomic defects, steps, grain boundaries and other surface irregularities and ultimately to probe the unknown mechanism causing superconductivity in the high-transition temperature (Tc) superconductors. The project will support the training of graduate students and postdoctoral students in areas of continuing scientific and technological significance, including low-temperature physics, scanning near-field microscopy, materials physics and superconducting devices. The project will work to increase the participation of women and minorities in the physical sciences, improve undergraduate and graduate education in physics, and foster collaborations with scientists from Latin America and Eastern Europe.