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  1. Critical Dynamics of Electron-Doped Cuprate SuperconductorsMatthew C. Sullivan, Ithaca College, DMR 0706557 We are studying the electron-doped cuprate Pr2-xCexCuO4 (PCCO) in hopes of understanding the differences and similarities between the electron-doped and hole-doped cuprates. We are studying the critical dynamics of the normal-superconducting phase transition, looking for the dynamic and static critical exponents. We have found that, contrary to expectations, PCCO does not behave in the same manner as the hole-doped cuprates. Rather than being governed by critical behavior near the phase transition, the large transition width of these films means that they behave like conventional superconductors and obey mean-field theory. Only when transitions widths are very small does z approach z=1.5, similar to exponents found in hole-doped cuprates. This research was published in Physical Review B in 2010. We are currently studying the critical current density in hole-doped YBa2Cu3O7-δ (YBCO) to compare its behavior with PCCO. We find that YBCO exhibits both mean-field and critical behavior, and effect not seen before in this material. On the left, the dynamic critical exponent z as a function of transition width, indicating conventional, mean-field behavior for large transition widths. On the right, the static critical exponent. The upper line is the critical prediction, the lower line is the mean-field prediction. We find that PCCO behaves like a conventional superconductor. Critical current density in YBCO. We find a crossover between critical behavior (red line) to mean-field behavior (green line).

  2. Critical Dynamics of Electron-Doped Cuprate SuperconductorsMatthew C. Sullivan, Ithaca College, DMR 0706557 Physics undergraduate students (from left): Romaine Isaacs, Emily Backus, and Arnold Kotlyarevsky. All three students presented their research at the American Physical Society March Meeting in Portland, OR, where we also visited Intel. On the right are Andrew Hope and Taylor Boyd, who worked on growing crystals for outreach demonstrations. During 2009-2010, four undergraduate students trained in and worked on various aspects of modern experimental low temperature research, including thin film growth and photolithography. These students included two students in underrepresented groups. We have also increased our outreach efforts. We created a program titled “Temperature and Heat” which we brought to three different local schools during 2009-2010. We have also worked on trying to reach the today’s audience. Our YouTube videos have received more than 56,000 views. A manuscript describing this demonstration (with an undergraduate first author) has been published in the American Journal of Physics. videos: