Electronic and transport properties in Ruddlesden-Popper neodymium nickelates Ndn+1NinO3n+1 (

A series of Ruddlesden-Popper nickelates ${\mathrm{Nd}}_{n+1}{\mathrm{Ni}}_{n}{\mathrm{O}}_{3n+1}$ ($n=1--5$) have been stabilized in thin film form using reactive molecular-beam epitaxy. X-ray diffraction and scanning transmission electron microscopy measurements suggest high crystalline quality of these films. The average Ni valence states in these compounds are in accordance with the nominal values, as verified by x-ray photoelectron spectroscopy. The metal-insulator transition temperature (${T}_{\mathrm{MI}}$) shows a clear $n$ dependence for $n=3--5$ members. At low temperature, the resistivity for $n=3--5$ members exhibits a log $T$ dependence, which is like that reported in parent compounds of superconducting infinite-layer nickelates.