Juan Gabriel Ramírez

The escalating energy demands of modern artificial intelligence have exposed fundamental limitations in conventional computing architectures. Neuromorphic computing, which seeks to emulate the brain’s massively parallel and energy-efficient information processing, offers a compelling alternative, but its realization requires materials that naturally exhibit nonlinear, multi-state, and adaptive behavior characteristic of biological neurons and synapses. This review argues that strongly correlated electron materials, particularly Mott insulators, provide exactly this physical substrate. We present the essential physics of metal-insulator transitions in vanadium oxides (VO2, V2O3) and perovskite manganites in an accessible manner and describe how their switching behaviors map onto neuromorphic primitives: the neuristor (artificial neuron) and the synaptor (artificial synapse). The review draws extensively on the authors’ experimental work: direct imaging of nanotextured phase coexistence in V2O3; an MIT Fingerprinting approach to engineer multi-state resistive switching in VO2; the demonstration of subthreshold firing in Mott nanodevices; and 1 electrically controlled multi-state analog memory in phase-separated manganites. The review concludes by identifying the main challenges and the most promising directions to translate these laboratory demonstrations into practical brain-inspired computing systems.

La transición metal-aislante (MIT) en el dióxido de vanadio (VO2) representa un sistema canónico de electrones correlacionados donde correlaciones electrónicas y distorsiones estructurales operan cooperativamente. Presentamos una metodología experimental para deconvolucionar las vías de conmutación electrónica y térmica mediante mediciones pulsadas corriente-voltaje dependientes de temperatura, minimizando efectos de auto-calentamiento. El espectro de conmutación se descompone en ramas electrónicas (débil dependencia térmica) y ramas térmicas (dependencia parabólica, calentamiento Joule). Las ramas electrónicas identificadas permiten aplicaciones en memorias neuromórficas y osciladores de alta frecuencia. Este trabajo proporciona evidencia experimental directa de la operación simultánea de ambos mecanismos, estableciendo un marco cuantitativo para transiciones de fase impulsadas por voltaje en óxidos correlacionados.

The voltage control of spin and charge degrees of freedom in complex materials is a cornerstone for the realization of advanced electronic devices with enhanced functionalities. Here, we demonstrate in situ indirect current control via the Joule effect of the spin resonance parameters in a phase-separated La5/8−yPryCa3/8MnO3 sample while simultaneously inducing resistive switching. By employing electron paramagnetic resonance (EPR) spectroscopy under an applied bias voltage, we observe sharp, reversible modifications in the EPR spectra—linewidth, resonance field, and intensity—concurrent with voltage-driven transitions between the ferromagnetic metallic (FMM) and paramagnetic charge-ordered (PM-CO) states. This real-time probing of spin resonance during resistive switching provides crucial insights into the interplay between spin, charge, and lattice degrees of freedom, elucidating the distinct roles of the FMM and PM-CO phases in the observed behavior. These findings pave the way for the development of novel spintronic and neuromorphic devices with voltage-tunable functionalities.

We report on the synthesis and characterization of V₂O₅ nanoparticles grown using a sol–gel method at different calcination temperatures. We observed a surprising reduction in the optical band gap from 2.20 to 1.18 eV with increasing calcination temperature from 400 to 500 °C. Raman and X-Ray diffraction measurements indicated slight changes in the lattice parameters induced by the growth process. However, density functional theory calculations of the Rietveld-refined and pristine structures revealed that the observed optical gap reduction could not be explained by structural changes alone. By introducing oxygen vacancies to the refined structures, we could reproduce the reduction of the band gap. Our calculations also showed that the inclusion of oxygen vacancies at the vanadyl position creates a spin-polarized interband state that reduces the electronic band gap and promotes a magnetic response due to unpaired electrons. This prediction was confirmed by our magnetometry measurements, which exhibited a ferromagnetic-like behavior. Our findings suggest that oxygen vacancies play a crucial role in band gap reduction and the promotion of a ferromagnetic-like response in an otherwise paramagnetic material. This provides a promising route to engineer novel devices.

For the past eight decades, understanding the physical mechanisms that occur at the interface between two different materials has been an open question driven by the breaking of crystalline symmetry and the reduction of atomic coordination, which modify the type and orbital occupation of atoms in the interface. Surface science began studying interface phenomena and has advanced significantly thanks to new and sophisticated tools for controlled fabrication and monolayer characterization. This focus has stimulated scientific and technological advancements, especially in the context of electronic devices and a wide range of interdisciplinary applications, such as biointerfaces, next-generation ultrasensitive detectors and actuators, and improved tribological properties. Here we provide a historical context of emerging interfacial phenomena and their influence on properties exhibited in junctions, multilayers, and heterostructures. We discuss advances in magnetic superlattice systems that enhance the information density of hard drives. We also explore electronic and magnetic interface states, as well as new functionalities in interfaces within heterojunctions based on complex oxides. Finally, we highlight advances and perspectives in surface science. En las últimas ocho décadas la comprensión de los mecanismos físicos que ocurren en la superficie límite entre dos materiales diferentes ha estado en constante evolución. Su interés radica en la ruptura de la simetría cristalina y la reducción de la coordinación atómica, las cuales producen modificaciones en el tipo y la ocupación orbital de los átomos en la interfaz. El estudio de los fenómenos interfaciales dio inicio a la ciencia de superficies, cuyo avance ha sido significativo en la medida en que aparecen nuevas y sofisticadas herramientas, tanto para la fabricación controlada de interfaces, como para la caracterización en el rango de la monocapa atómica. El interés se ha centrado no solo en el estímulo científico si no en el tecnológico, sobre todo en el contexto de los dispositivos electrónicos y, más recientemente, en una amplia gama de aplicaciones interdisciplinarias, como las biointerfaces, los detectores y actuadores ultrasensibles de última generación y el mejoramiento de las propiedades tribológicas. En este trabajo presentamos, primero, un contexto histórico de los diferentes fenómenos interfaciales que han ido surgiendo y su influencia en las propiedades que exhiben donde quiera que hay una interfaz, como en el caso de junturas, multicapas y heteroestructuras. Presentamos, asimismo, los avances en los sistemas de superredes magnéticas de importancia en el mejoramiento de la densidad de información de los discos duros, y discutimos sobre los estados interfaciales electrónicos y magnéticos y las nuevas funcionalidades en las interfaces de heterojunturas basadas en óxidos complejos. Por último, resaltamos algunos avances y perspectivas en el campo de la ciencia de superficies.