Doping evolution and polar surface reconstruction of the infinite-layer cuprate Sr$_{1-x}$La$_{x}$CuO$_{2}$

We use angle-resolved photoemission spectroscopy to study the doping evolution of infinite-layer Sr$_{1-x}$La$_{x}$CuO$_{2}$ thin films grown by molecular-beam epitaxy. At low doping, the material exhibits a dispersive lower Hubbard band typical of the superconducting cuprate parent compounds. Electron diffraction probes reveal a $p(2\times2)$ reconstruction of the surface. Using a number of simple assumptions, we develop a model of this reconstruction based on the polar nature of the infinite-layer material. As carriers are added to the system, a continuous evolution from Mott insulator to superconducting metal is observed as a coherent low-energy band develops with a concomitant remnant lower Hubbard band, gradually filling in the Mott gap. This two-component spectral function emphasizes the important role that strong local electron correlations play in the electronic structure of Sr$_{1-x}$La$_{x}$CuO$_{2}$ even at relatively high doping levels. Finally, we confirm the theoretical prediction of a thickness-controlled transition in ultrathin films of SrCuO$_{2}$ grown on nonpolar SrTiO$_{3}$, highlighting the diverse structural changes that can occur in polar complex oxide thin films.