A novel route to hole-doping epitaxial thin films: Sr$_{2-x}$K$_{x}$IrO$_4$

The layered, two-dimensional antiferromagnetic insulator Sr$_2$IrO$_4$ has been the subject of intense investigation, in large part due to its strong similarity to the prototypical layered parent cuprate La$_2$CuO$_4$. As both electron and hole doping the parent cuprates result in high-temperature superconductivity, carrier doping Sr$_2$IrO$_4$ has likewise been an important goal in the study of layered iridates. While the electron-doped side of Sr$_2$IrO$_4$ (either by surface K doping or La substitution) has been well explored, the hole-doped side of the phase diagram has been less studied. While substituting Rh on the Ir has been shown to result in hole-doping, this also induces significant disorder to the IrO$_2$ planes. Here, we present a new method to synthesize hole-doped Sr$_{2-x}$K$_{x}$IrO$_4$ by a combination of reactive oxide molecular beam epitaxy utilizing K substitution for Sr which induces much less disorder, resulting in well-defined quasiparticle bands and allowing us to observe a clear hole-doped Fermi surface topology with an intrinsic momentum-dependent pseudogap.