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Many correlated systems feature an insulator-to-metal transition that can be triggered by an electric field. Although it is known that metallization takes place through filament formation, the details of how this process initiates and evolves remain elusive. We use in-operando optical reflectivity to capture the growth dynamics of the metallic phase with space and time resolution. We demonstrate that filament formation is triggered by nucleation at hotspots, with a subsequent expansion over several decades in time. By comparing three case studies (VO2, V3O5 and V2O3), we identify the resistivity change across the transition as the crucial parameter governing this process. Our results provide a spatiotemporal characterization of volatile resistive switching in Mott insulators, key for emerging technologies such as optoelectronics or neuromorphic computing.

The interdependences of different phase transitions in Mott materials are fundamental to the understanding of the mechanisms behind them. One of the most important relations is between the ubiquitous structural and electronic transitions. Using IR spectroscopy, optical reflectivity and x-ray diffraction we show that the metal-insulator transition (MIT) is coupled to the structural phase transition in V2O3 films. This coupling persists even in films with widely varying transition temperatures and strains. Our findings are in contrast to recent experimental findings and theoretical predictions. Using V2O3 as a model system, we discuss the pitfalls in measurements of the electronic and structural states of Mott materials in general, calling for a critical examination of previous work in this field. Our findings also have important implications for the performance of Mott materials in next-generation neuromorphic computing technology.

Strain engineering is a well-known method often used to tune material properties in thin films. The most studied sources of strain are lattice mismatch and differential thermal contraction between the substrate and film. However, in materials which undergo a structural phase transition (SPT), a third and often overlooked source of strain may play a very significant role. If the substrate confines the area of the film, the SPT may induce stress which changes the evolution of the transition. This is a 2D analog of the isochoric phase transition between water and ice, where the freezing point drops below 0 °C. To illustrate this, the prototypical Mott insulator V 2 O 3 which has an SPT coupled to a metal-insulator transition is used to show how self-induced strain can drastically alter structural and electronic properties. This effect provides an elegant approach for mapping the phase diagram of the SPT and the transitions coupled to it. Moreover, the magnitude of self-straining is tunable by modifying the substrate morphology. This effect may be important for numerous materials which exhibit an SPT and are subjected to geometrical constraints.

Artículo de publicación ISIWe have used Monte Carlo simulations to investigate the magnetic properties of asymmetric dots as a function of their geometry. The asymmetry of round dots is produced by cutting off a fraction of the dot and is characterized by an asymmetry parameter . This shape asymmetry has interesting effects on the coercivity (Hc), remanence (Mr), and barrier for vortex and C- state formation. The dependences of Hc and Mr are non monotonic as a function of with a well defined minima in these parameters. The vortex enters the most asymmetric part and exits through the symmetric portion of the dot. With increasing the vortex formation starts with a C-state which persists for longer fields and the barrier for vortex exit diminishes with increasing asymmetry, thus providing control over the magnetic chirality. This implies interesting, naively-unexpected, magnetic behavior as a function of geometry and magnetic field

The possibility of a three-state nanoelement, composed by a wire and a tube, is investigated by means of Monte Carlo simulations. The desired behavior may be identified by a step or plateau in the hysteresis curve, corresponding to a partial pinning of the domain wall at the interface between wire and tube sections. This step may be augmented in segmented nanoelements with large coercivity difference between the sections. Different possibilities, such as geometry and choice of materials, are explored.

The high-power consumption caused by Joule heating is one reason for the emergence of the research area of neuromorphic computing. However, Joule heating is not only detrimental. In a specific class of devices considered for emulating firing of neurons, the formation of an electro-thermal filament sustained by locally confined Joule heating accompanies resistive switching. Here, the resistive switching in a V2O3-thin-film device is visualized via high-resolution wide-field microscopy. Although the formation and destruction of electro-thermal filaments dominate the resistive switching, the strain-induced coupling of the structural and electronic degrees of freedom leads to various unexpected effects like oblique filaments, filament splitting, memory effect, and a hysteretic current-voltage relation with saw-tooth like jumps at high currents. Main Text:The strongly correlated electron system (SCES) V2O3 is a prototypical Mott-Hubbard insulator [1]. At room temperature, stoichiometric V2O3 is a paramagnetic metal with corundum structure, which undergoes a metal-to-insulator-transition (MIT) in cooling below about 150 K. The insulating phase is antiferromagnetic with monoclinic structure.Upon heating the insulating phase undergoes an insulator-to-metal-transition (IMT) [2][3][4]. In recent years, there has been a growing interest in the resistive switching of SCES-devices [5].

The coupling of electronic degrees of freedom in materials to create "hybridized functionalities" is a holy grail of modern condensed matter physics that may produce versatile mechanisms of control. Correlated electron systems often exhibit coupled degrees of freedom with a high degree of tunability which sometimes lead to hybridized functionalities based on external stimuli. However, the mechanisms of tunability and the sensitivity to external stimuli are determined by intrinsic material properties which are not always controllable. A Mott metalinsulator transition (MIT) is technologically attractive due to the large changes in resistance, tunable by doping, strain, electric fields, and orbital occupancy but not, in and of itself, controllable with light. Here, an alternate approach is presented to produce optical functionalities using a properly engineered photoconductor/strongly correlated hybrid heterostructure. This approach combines a photoconductor, which does not exhibit an MIT, with a strongly correlated oxide, which is not photoconducting. Due to the intimate proximity between the two materials, the heterostructure exhibits giant volatile and nonvolatile, photoinduced resistivity changes with substantial shifts in the MIT transition temperatures. This approach can be extended to other judicious combinations of strongly correlated materials.