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

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 118; no. 30; pp. 1 - 5
• Main Authors: Kim, Gideok, Rabinovich, Ksenia S., Boris, Alexander V., Yaresko, Alexander N., Suyolcu, Y. Eren, Wu, Yu-Mi, van Aken, Peter A., Christiani, Georg, Logvenov, Gennady, Keimer, Bernhard
• Format: Journal Article
• Language: English
• Published: Washington National Academy of Sciences 27.07.2021
• Subjects: Calcium ions; Conductivity; Cuprates; Epitaxial growth; Mean field theory; Molecular beam epitaxy; Phase diagrams; Physical Sciences; Spectroellipsometry; Superconductivity; Thin films
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2106170118

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 ∼ 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 Tc 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.