ARPES on Coherently Strained Ruddelsden-Popper Nickelate Thin Films

Since the discovery of high-T_c superconductivity in the Ruddelsden-Popper (RP) Nickelates La₃Ni₂O₇ and La₄Ni₃O₁₀ under high hydrostatic pressure, there has been great interest in determining the mechanism for this superconductivity. A key difference with cuprate superconductivity is the presence of d_z² bands near the Fermi energy in addition to the d_x²-y² bands, so finding a way to explore these under pressure is critical. It has been shown that the effects of high hydrostatic pressure can be mimicked by in-plane strain, which can be accomplished via epitaxial thin-film growth on various substrates. Here we report ARPES measurements collected on a series of substrate-strained RP nickelate thin films under both tensile and compressive strain. Quantitative changes are observed in several bands near the Fermi level.