On the preparation and the characterization of superconducting thin films of YBa2Cu3O7−x

The results of our initial efforts to deposit thin films of YBa₂Cu₃O_7−x system on sapphire substrate are described. The deposited films are shiny black in appearance and are of quite uniform chemical composition. The annealed films exhibit zero resistance superconducting transition temperatureT _c(R=0) ranging between 23 K and 30 K.     

The hall coefficient of YBa2Cu3O7-x thin films with (100) orientation

The Hall coefficientR _H and the resistivity of an (100) orientated YBa₂Cu₃O_7-x thin film was measured. A very smallR _H was obtained. The resulting carrier density is very different from the widely accepted value of the order of 10²¹ cm^–3 for the bulk sample. The result is explained with the influence of grain boundaries and the anisotropy of the thin films.     

Effect of YBa2Cu3O7-x thin films on the textures and orientational properties of liquid crystals

In the present work, the effect of thin films of YBa₂Cu₃O_7-x complex compound on the mesomorphic and orientational properties of thermotropic nematic liquid crystals has been studied. Homogeneous, stable and reproducible homeotropic and tilted oriented textures of nematic liquid crystals were obtained. The effect of YBa₂Cu₃O_7-x thin films on the morphologic, orientational and optical properties of thermotropic nematic liquid crystals are discussed.     

Indications of an electronic phase transition in two-dimensional superconducting YBa2Cu3O(7-x) thin films induced by electrostatic doping

We successfully tuned an underdoped ultrathin YBa2Cu3O(7-x) film into the overdoped regime by means of electrostatic doping using an ionic liquid as a dielectric material. This process proved to be reversible. Transport measurements showed a series of anomalous features compared to chemically doped bulk samples and a different two-step doping mechanism for electrostatic doping was revealed. The normal resistance increased with carrier concentration on the overdoped side and the high temperature (180 K) Hall number peaked at a doping level of p～0.15. These anomalous behaviors suggest that there is an electronic phase transition in the Fermi surface around the optimal doping level.