Molecular-beam epitaxy of SrMoO₃ films with record low electrical resistivity

SrMoO₃ (SMO) is the most conductive perovskite oxide with a room-temperature resistivity of ~5.1 μΩ-cm, about 40 times more conductive than SrRuO₃. This makes it an attractive material as a bottom electrode for perovskite heterostructures, particularly for the high-K dielectric Ba_xSr_1-xTiO_3, which is well lattice matched to SMO. Importantly, the properties of oxide conductors often depend strongly on composition, where off-stoichiometry can increase the room-temperature resistivity and dramatically decrease the residual resistivity ratio. This disorder is presumably responsible for the factor of 5 difference between the lowest room-temperature resistivity values obtained to date for SMO films compared to the best SMO bulk crystals. Here we report the properties of SMO thin films grown via Molecular Beam Epitaxy in an adsorption-controlled regime of substrate temperatures above 1100 °C, accessible by CO₂ laser heating, in which strontium oxide can be volatile. The resulting phase-pure epitaxial SMO thin films are characterized by narrow rocking curves, room-temperature resistivities under significantly lower than all prior epitaxial SMO films (and residual resistivity ratios better even than the best SMO single crystals reported to date. In situ angle-resolved photoemission measurements of these high-quality SMO films reveal remarkably sharp quasiparticles, allowing us to resolve subtle features in the spectra, such as band folding that arises from orthorhombic distortions.