Fractal Nature of Metallic and Insulating Domain Configurations in a VO2 Thin Film Revealed by Kelvin Probe Force Microscopy

Abstract

We investigated the surface work function (WS) and its spatial distribution for epitaxial VO2/TiO2 thin films using Kelvin probe force microscopy (KPFM). Nearly grain-boundary-free samples allowed observation of metallic and insulating domains with distinct WS values, throughout the metal–insulator transition. The metallic fraction, estimated from WS maps, describes the evolution of the resistance based on a two-dimensional percolation model. The KPFM measurements also revealed the fractal nature of the domain configuration.

Scale-invariant magnetic textures in the strongly correlated oxide NdNiO3

“…Details of the fitting results for each map are described in the Supplementary Table 1. These observations of non-integral exponents and scale-free distribution altogether point to an unexpected fractal nature of AFM domains in NdNiO 3 [8,21,29,33,47].…”

“…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.…”

Visualization of local phase transition behaviors near dislocations in epitaxial VO2/TiO2 thin films

“…[http://dx.doi.org/10.1063/1.4934943] VO 2 shows a tetragonal-monoclinic structural phase transition (SPT) as well as a metal-insulator transition (MIT) near room temperature. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Due to this unique feature, both Mott transition and Peierls instability have been considered as key theoretical components in explaining this intriguing phase transition phenomenon. [1][2][3][4][5][6][7][8][9] The structural distortion, occurring during the SPT, affects the orbital occupancy which directly changes the electron-electron correlation.…”

“…[6][7][8][9][10] Thus, strain states of VO 2 can significantly modify the MIT behaviors, as reported in many thin film studies; additionally, strain states can be controlled by varying the substrates and/or thickness of the samples. [7][8][9][10][11][12][13][14][15] Thick films, especially samples with a large lattice mismatch, may have nonuniform strain states and contain structural defects. [10][11][12][13][14] Local phase transition behaviors may vary depending on the lattice spacing at specific locations and the interaction with nearby regions.…”

Tailoring Vanadium Dioxide Film Orientation Using Nanosheets: a Combined Microscopy, Diffraction, Transport, and Soft X‐Ray in Transmission Study

“…A possible explanation for this observation could be related to the fact that the NWO‐templated VO 2 possesses a surface roughness of order 10 nm, compared to 2 nm for the TO‐templated VO 2 films (see Figure S1 (Supporting Information) for AFM data from the VO 2 films). As the MIT in VO 2 possesses a strongly percolative character, the increased roughness, on top of an increased density of grain boundaries due to inter‐nanosheet boundaries can be at least a partial explanation of the broader transition for the case of VO 2 grown on NWO nanosheet templates. In addition, the larger deviation from 90° bond angles of the 2D atomic structure of the (−402) M1 plane in the NWO case compared to the (011) M1 plane for TO‐templated growth (see Figure ) is also compatible with a larger domain/grain boundary contribution to the transport for the NWO‐templated VO 2 .…”