Abstract
We report the epitaxial growth of Ruddlesden–Popper nickelates, Lan+1NinO3n+1, with n up to 5 by reactive molecular beam epitaxy. X-ray diffractions indicate high crystalline quality of these films, and transport measurements show strong dependence on the n values. Angle-resolved photoemission spectroscopy reveals the electronic structure of La5Ni4O13, showing a large hole-like pocket centered around the Brillouin zone corner with a (π, π) back-folded copy.
Highlights
Layered perovskite nickelates have long been considered as close analogs to high Tc cuprates and have been extensively studied by theoretical and experimental investigations for potential new superconductors.1–3 Recently, remarkable progress has been achieved by Li and his collaborators in the synthesis and observation of superconductivity in Sr doped infinite-layer nickelate NdNiO2,4,5 which has been reproduced by other groups.6,7 NdNiO2 is synthesized by removing the apical oxygen atoms of the perovskite NdNiO3 through a careful reduction process employing CaH2.4,6In addition to the infinite-layer compound, the n = ∞ member of the Ruddlesden–Popper (RP) phases (Lnn+1NinO3n+1, Ln: rare earth elements), the other RP members are natural candidates to be explored for high Tc superconductivity
By extracting the oscillation period from more than 10 oscillation cycles, precise shutter times for La and Ni sources were obtained. Based on these monolayer dosages calibrated by a co-deposition method, RP nickelates of any n value can be synthesized by depositing LaO and NiO2 layers alternatively in the desired sequences using a shutter-control mode
There exists a clear (π, π) back-folded copy of the hole-like band, which is similar to cuprates37–40 and La4Ni3O1034 but different from LaNiO3.24 This band folding is consistent with the superlattice diffractions observed in the low energy electron diffraction (LEED) pattern [Fig. 4(a)] and most likely due to the lattice reconstruction driven by NiO6 octahedral rotations
Summary
The homologous series of high Tc cuprates exhibits a clear dependence of the superconducting transition temperature with a number of layers in their layered structure,8–10 making it more tempting to investigate the RP nickelates with higher n values. X-ray diffraction (XRD) indicates the high crystalline quality of these films, and transport measurements show a strong dependence on the n value.
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