Direct Mapping of Phase Separation across the Metal–Insulator Transition of NdNiO₃

Abstract

Perovskite rare-earth nickelates RNiO are prototype correlated oxides displaying a metal-insulator transition (MIT) at a temperature tunable by the ionic radius of the rare-earth R. Although its precise origin remains a debated topic, the MIT can be exploited in various types of applications, notably for resistive switching and neuromorphic computation. So far, the MIT has been mostly studied by macroscopic techniques, and insights into its nanoscale mechanisms were only provided recently by X-ray photoemission electron microscopy through absorption line shifts, used as an indirect proxy to the resistive state. Here, we directly image the local resistance of NdNiO thin films across their first-order MIT using conductive-atomic force microscopy. Our resistance maps reveal the nucleation of ∼100-300 nm metallic domains in the insulating state that grow and percolate as temperature increases. We discuss the resistance contrast mechanism, analyze the microscopy and transport data within a percolation model, and propose experiments to harness this mesoscopic electronic texture in devices.

Imaging and Harnessing Percolation at the Metal–Insulator Transition of NdNiO3 Nanogaps

“…The detailed growth conditions can be found in previous references 20,25 . Following the NNO film deposition, a PMMA A6 resist soft-mask was prepared with e-beam lithography.…”

“…where full G corresponds to the full heating curve obtained from the experiment, and D is the dimension of our system set to be 2. This two-dimensional approximation seems reasonable since the film thickness is only ~4 nm 23 and the size of M-phase domains is about two orders of magnitude higher 19,20 . In Fig.…”

Scale-invariant magnetic textures in the strongly correlated oxide NdNiO3

“…When these electronic phases compete, they segregate at nano-or mesoscopic length scales, giving rise to complex, multiscale domain textures [4][5][6]. Nowadays, there is overwhelming evidence of domain pattern formation for an array of emergent phenomena, including metal-insulator transitions [7][8][9][10][11], charge/magnetic ordering [12][13][14], and unconventional superconductivity [15][16][17]. Several studies have identified these spatial textures as essential underpinnings for novel phenomena in TMOs and other correlated electron [5,13,[18][19][20][21].Rare earth nickelates (RENiO 3 ) are a fertile platform to realize and explore the emergent physics brewing in proximity to electronic symmetry-breaking phenomena, thanks to the cooperative action of the coupled charge, spin, and lattice degrees of freedom.…”

Spatial and spectral dynamics in STEM hyperspectral imaging using random scan patterns

“…More details on the interface growth and specimen preparation can be found in Ref. 21. Atomically-resolved EELS mapping was performed on a Nion UltraSTEM 200 microscope operated at 100 keV.…”