Epitaxial growth of Ruddlesden-Popper neodymium nickelates Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$ = 1-5)

TL;DR

This study reports the successful epitaxial growth and characterization of Ruddlesden-Popper Nd nickelates with varying layers, revealing their structural, electronic, and transport properties, including metal-insulator transitions and Kondo-like behavior.

Contribution

It introduces a method to synthesize high-quality thin films of Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ with detailed analysis of their properties, expanding understanding of layered nickelates.

Findings

High crystalline quality of films confirmed by X-ray diffraction and electron microscopy.

Valence states of nickel depend on the layer number n.

Metal-insulator transitions observed for n=3-5, with low-temperature resistivity showing Kondo-like logarithmic dependence.

Abstract

A series of Ruddlesden-Popper nickelates, Nd$_{n+1}$Ni$_{n}$O$_{3n+1}$ (${n}$ = 1-5), have been stabilized in thin film form using reactive molecular-beam epitaxy. High crystalline quality has been verified by X-ray diffraction and scanning transmission electron microscopy. X-ray photoelectron spectroscopy indicates the ${n}$-dependent valence states of nickel in these compounds. Metal-insulator transitions show clear ${n}$ dependence for intermediate members (${n}$ = 3-5), and the low-temperature resistivities of which show logarithmic dependence, resembling the Kondo-scattering as observed in the parent compounds of superconducting infinite-layer nickelates.