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

Photoassisted Electron-Ion Synergic Doping Induced Phase Transition of n-VO2/p-GaN Thin-Film Heterojunction

As a typical correlated metal oxide, vanadium dioxide (VO₂) shows specific metal-insulator transition (MIT) properties and demonstrates great potential applications in ultrafast optoelectronic switch, resistive memory, and neuromorphic devices. Effective control of the MIT process is essential for improving the device performance. In the current study, we have first proposed a photoassisted ion-doping method to modulate the phase transition of the VO₂ layer based on the photovoltaic effect and electron-ion synergic doping in acid solution. Experimental results show that, for the prepared n-VO₂/p-GaN nanojunction, this photoassisted strategy can effectively dope the n-VO₂ layer by H⁺, Al³⁺, or Mg²⁺ ions under light radiation and trigger consecutive insulator-metal-insulator transitions. If combined with standard lithography or electron beam etching processes, selective doping with nanoscale size area can also be achieved. This photoassisted doping method not only shows a facile route for MIT modulation via a doping route under ambient conditions but also supplies some clues for photosensitive detection in the future.

Nucleation and Growth Bottleneck in the Conductivity Recovery Dynamics of Nickelate Ultrathin Films

We investigate THz conductivity dynamics in NdNiO₃ and EuNiO₃ ultrathin films (15 unit cells, u.c., ∼5.7 nm thick) following a photoinduced thermal quench into the metallic state and reveal a clear contrast between first- and second-order dynamics. While in EuNiO₃ the conductivity recovers exponentially, in NdNiO₃ the recovery is nonexponential and slower than a simple thermal model. Crucially, it is consistent with first-order dynamics and well-described by a 2d Avrami model, with supercooling leading to metastable phase coexistence on the nano- to mesoscopic scale. This novel observation is a fundamentally dynamic manifestation of the first-order character of the insulator-to-metal transition, which the nanoscale thickness of our films and their fast cooling rate enable us to detect. The large transients seen in our films are promising for fast electronic (and magnetic) switching applications.

Switchable metal-insulator transition in core-shell cluster-assembled nanostructure films

Fe/Fe3O4 core-shell-cluster-assembled nanostructured films were prepared using the low-energy cluster beam deposition technique. The temperature-dependent resistivity behaviors were investigated for the films with changing core-occupation ratio of clusters. Much interestingly and surprisingly, a switchable metal-insulator transition can be observed, featuring the rapid switching from the metal state to the insulation state and then back to the metal state, for films within a specific range of core-occupation ratio. Further, the resistivity change rate used to characterize the metal-insulator transition can reach as high as two orders of magnitude over a very narrow temperature region. The design of Fe/Fe3O4 core-shell clusters plays a decisive role in the mechanism of the switchable metal-insulator transition in these films. The assembled core-shell clusters in the films form current conduction channels that are switchable between the cores and shells of clusters as the temperature changes. The switching of the current conduction channels can be regulated by controlling the core-occupation ratios of clusters, which induce a switchable metal-insulator transition and can be verified by the effective medium theory over a specific core-occupation ratio range.

Investigation of Statistical Metal-Insulator Transition Properties of Electronic Domains in Spatially Confined VO2 Nanostructure

Functional oxides with strongly correlated electron systems, such as vanadium dioxide, manganite, and so on, show a metal-insulator transition and an insulator-metal transition (MIT and IMT) with a change in conductivity of several orders of magnitude. Since the discovery of phase separation during transition processes, many researchers have been trying to capture a nanoscale electronic domain and investigate its exotic properties. To understand the exotic properties of the nanoscale electronic domain, we studied the MIT and IMT properties for the VO2 electronic domains confined into a 20 nm length scale. The confined domains in VO2 exhibited an intrinsic first-order MIT and IMT with an unusually steep single-step change in the temperature dependent resistivity (R-T) curve. The investigation of the temperature-sweep-rate dependent MIT and IMT properties revealed the statistical transition behavior among the domains. These results are the first demonstration approaching the transition dynamics: the competition between the phase-transition kinetics and experimental temperature-sweep-rate in a nano scale. We proposed a statistical transition model to describe the correlation between the domain behavior and the observable R-T curve, which connect the progression of the MIT and IMT from the macroscopic to microscopic viewpoints.