Epitaxial growth of hexagonal tungsten bronze CsxWO3 films in   superconducting phase region exceeding bulk limit
  We report epitaxial synthesis of superconducting CsxWO3 (x = 0.11, 0.20, 0.31) films on Y-stabilized ZrO2 (111) substrates. The hexagonal crystal structure was verified not only for composition within the stable region of bulk (x = 0.20, 0.31), but also for the out-of-range composition (x = 0.11). The onset of superconducting transition temperature (TC) was recorded 5.8 K for x = 0.11. We found strong correlation between TC and c-axis length, irrespective of the Cs content. The results indicate that hidden superconducting phase region of hexagonal tungsten bronze is accessible by using epitaxial synthesis of lightly doped films. 
Takuto Soma, Kohei Yoshimatsu, and Akira Ohtomo
cond-mat.mtrl-sci