Electrostatic Doping of Novel Materials

Field effect transistor configurations have been employed as electrostatic alternatives to chemical doping of novel materials. They provide exquisite control of material properties, which may include magnetism and superconductivity.  The technique can be used to tune the superconductor-to–insulator transition.  A recent innovation has been to replace the gate insulator, which is usually a high-dielectric constant material, with an ionic liquid. Ionic liquids are molten salts at room temperature. When used as a gate dielectric, ionic liquids can facilitate extraordinarily large charge transfers because of the formation of an electronic double layer, which is in effect a capacitor with a nanometer scale gap.  Recent work involving ultrathin YBa2Cu3O7−x(YBCO) films gate using electronic double layer transistor configurations involving ionic liquids as gate dielectrics will be discussed.  In essence the entire phase diagram of the compound can be traversed.  In principle electrostatic gating using ionic liquids may provide an alternative approach to searching for new superconductors as it may serve as a means of systematically doping putative parent compounds. 

* Supported in part by the NSF under grants NSF/DMR-0709584 and 0854752 and performed in collaboration with Xiang Leng, Javier Garcia-Barriocanal, Joseph Kinney and Boyi Yang.