1. Indications of an Electronic Phase Transition in 2D YBa2Cu3O7-xAllen M. Goldman, University of Minnesota-Twin Cities, DMR 0854752 The properties of ultrathin YBa2Cu3O7-x (YBCO) high-Tc films have been modified by electrostatic charging using a field effect transistor (FET) configuration employing an ionic liquid as the dielectric. This configuration makes possible the transfer enormous levels of charge to the superconductor. Previously the evolution from superconductor to insulator was observed by depleting carriers. The newest work involves the accumulation of carriers by the removal of electrons. Measurements of electrical resistance were accompanied by Hall effect measurements which revealed a peak in the hole number at charge concentrations close to those corresponding to optimal doping. This suggests the occurrence of an electronic phase transition near optimal doping. Fig. 1. Transition temperature vs. hole concentration with holes accumulated using an EDLT employing an ionic liquid. The doping takes the system over the top of the super-conducting dome. Fig. 2. Normalized Hall number vs. effective carrier concentration. The peak in the Hall number is found at a carrier concentration slightly smaller than that corresponding to the maximum of Tc in Fig. 1.

2. Indications of an Electronic Phase Transition in 2D YBa2Cu3O7-Allen M. Goldman, University of Minnesota-Twin Cities, DMR 0854752 This work involved work of a postdoctoral student, Dr. Javier Garcia Barriocanal, whose salary was supported by the Fulbright program and the Spanish government. This helped to internationalize the laboratory. Xiang Leng was the graduate student involved in the program. Undergraduates participated in the early stages of the work. This work is one of the few quantitative studies involving the use of what are known as electronic double layer transistors (EDLTs) using ionic liquids (ILs) to modify the properties of a strongly correlated electron system. These EDLT configurations with ILs may be useful in the search for new superconductors and may be an alternative to chemical doping of parent compounds. This approach may greatly speed up the search for new superconductors. Please insert an image or group of images here to illustrate your broader impacts activities. If you need more space, you may reduce the adjacent textbox. Please use lettering that is clearly visible (i.e. not too small). Please include a brief figure caption. These are the individuals who, along with the PI, were the principle authors of the work described in this highlight. On the left is Dr. Javier Garcia-Barriocanal, who is now a faculty member at Complutense University in Madrid, Spain. The person on the right is Mr. Xiang Leng, who was a physics graduate student at the University of Minnesota. He is currently a postdoc in physics at Brookhaven National Laboratory in the group of Ivan Bozovic.