Optical conductivity and superconductivity in highly overdoped La2-xCaxCuO4 thin films

We have used atomic layer-by-layer oxide molecular beam epitaxy to grow epitaxial thin films of La2-xCaxCuO4 with x up to 0.5, greatly exceeding the solubility limit of Ca in bulk systems (x similar to 0.12). 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 T-c of 15 to 20 K up to the highest doping levels and attribute the unusual stability of superconductivity in La2-xCaxCuO4 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.

Automated summary

By using atomic layer-by-layer oxide molecular beam epitaxy, epitaxial thin films of La2-xCaxCuO4 with x up to 0.5 were successfully grown, exhibiting superconductivity with Tc of 15 to 20 K. The nearly identical radii of La and Ca ions in the material were found to minimize the impact of structural disorder, leading to an extended superconducting dome in the phase diagram of cuprates.