Publications by authors named "Nicolas Vargas"
Formic acid is unique among liquid organic hydrogen carriers (LOHCs), because its dehydrogenation is highly entropically driven. This enables the evolution of high-pressure hydrogen at mild temperatures that is difficult to achieve with other LOHCs, conceptually by releasing the "spring" of energy stored entropically in the liquid carrier. Applications calling for hydrogen-on-demand, such as vehicle filling, require pressurized H.
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- Strong electron repulsion in solids can lead to a phenomenon called the "Mott" metal-to-insulator transition (MIT), where electrons transform from a mobile to a localized state.
- Understanding this transition has been difficult for over 50 years due to challenges in observing both electronic states.
- Researchers used angle-resolved photoemission spectroscopy (ARPES) to demonstrate that in vanadium oxide (VO), increasing temperature causes the itinerant conduction band to vanish while a quasi-localized state shifts to higher binding energies.
In a spintronic resonator a radio-frequency signal excites spin dynamics that can be detected by the spin-diode effect. Such resonators are generally based on ferromagnetic metals and their responses to spin torques. New and richer functionalities can potentially be achieved with quantum materials, specifically with transition metal oxides that have phase transitions that can endow a spintronic resonator with hysteresis and memory.
View Article and Find Full Text PDFMany 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.
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- Resistive switching allows devices to alter their resistance with an electric field, playing a key role in new tech like neuromorphic computing and resistive memories.
- Threshold firing, a promising type of resistive switching found in Mott insulators, occurs when a material transitions from an insulating to a conducting state after reaching a certain voltage.
- Research shows that Mott nanodevices can 'remember' previous resistive switching events even after returning to the insulating state, and can be re-triggered using lower voltages for an extended period, highlighting a new form of volatile memory with various potential applications.
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 is coupled to the structural phase transition in V_{2}O_{3} films.
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