Disentangling Pseudogap from Superconductivity in the Cuprates by Scanning Tunneling Microscopy

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****TECHNICAL ABSTRACT****The nature and behavior of electronic states in high temperature superconductors (HTS) are the center of much debate. The pseudogap state, observed above the superconducting transition temperature, is seen by some as a precursor to the superconducting state. Others view it as a competing phase. Despite much experimental and theoretical work, this question remains highly debated and central to our understanding of HTS in general. This individual investigator award supports the investigation of this relationship by temperature dependent scanning tunneling microscopy (STM). Experiments will be performed in both Bi2Sr2CuO6+x, in which we have previously observed evidence for a competing phase, and YBa2Cu3O6+x, which is more commonly studied but has not been investigated with recently developed STM techniques. Ultrahigh vacuum, variable temperature scanning tunneling microscopy is a demanding experimental technique; HTS, as part of the broad class of strongly correlated electron systems, are at the center of much condensed matter physics. Hence this project will be an excellent training ground for students. Furthermore, this award will support science outreach to broad audiences driven by the compelling scientific mystery and technological promise of high temperature superconductivity.****NON-TECHNICAL ABSTRACT****Superconductors are materials that can carry current without resistance and resultant energy losses through heat generation. Unfortunately, this technologically useful property only turns on at very low temperatures, below a "transition temperature." Just over twenty years ago a new class of "High Temperature Superconductors" were discovered, with transition temperatures near 100 K. This is still very cold compared to room temperature (300 K), but has led to intense technological, such as energy infrastructure, and scientific development. This individual investigator award supports the experimental investigation of high temperature superconductors with the goal of understanding the relationship between their unconventional properties above the transition temperature (even above room temperature in some materials) and superconductivity. It has been proposed that these higher temperature properties compete, or interfere, with superconductivity, and that by understanding and controlling them transition temperatures may be significantly increased. While investigating this proposal, students will be trained in a wide range of experimental techniques. Furthermore, the compelling scientific mystery and technological promise of high temperature superconductivity enables scientific outreach to broad audiences, also supported by this award.