Optical conductivity and superconductivity in highly overdoped La2-x Ca x CuO4 thin films.

ABSTRACT

We have used atomic layer-by-layer oxide molecular beam epitaxy to grow epitaxial thin films of [Formula see text] with x up to 0.5, greatly exceeding the solubility limit of Ca in bulk systems ([Formula see text]). A comparison of the optical conductivity measured by spectroscopic ellipsometry to prior predictions from dynamical mean-field theory demonstrates that the hole concentration p is approximately equal to x. We find superconductivity with [Formula see text] of 15 to 20 K up to the highest doping levels and attribute the unusual stability of superconductivity in [Formula see text] to the nearly identical radii of La and Ca ions, which minimizes the impact of structural disorder. We conclude that careful disorder management can greatly extend the "superconducting dome" in the phase diagram of the cuprates.