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Reconfigurable devices offer the ability to program electronic circuits on demand. Here, in this work, we demonstrated on-demand creation of artificial neurons, synapses, and memory capacitors in post-fabricated perovskite NdNiO₃ devices that can be simply reconfigured for a specific purpose by single-shot electric pulses. The sensitivity of electronic properties of perovskite nickelates to the local distribution of hydrogen ions enabled these results. With experimental data from our memory capacitors, simulation results of a reservoir computing framework showed excellent performance for tasks such as digit recognition and classification of electrocardiogram heartbeat activity. Using our reconfigurable artificial neurons and synapses, simulated dynamicmore » networks outperformed static networks for incremental learning scenarios. The ability to fashion the building blocks of brain-inspired computers on demand opens up new directions in adaptive networks.« less

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The elementary basis of intelligence in organisms with a central nervous system includes neurons and synapses and their complex interconnections forming neural circuits. In non-neural organisms such as slime mold with gel-like media, viscosity modulation enables adaptation to changing environments. At a larger scale, collective intelligence emerges via social interactions and feedback in animal colonies. Learning and memory are therefore multi-scale features that evolve as a result of constant interactions with the environment. There is growing interest in emulating such features of intelligence in computing machines and autonomous systems. Materials that can respond to their environment in a manner similarmore » to organisms (referred to as "organismic materials") therefore may be of interest as hardware components in artificial intelligence machines. In this brief review, we present a class of semiconductors called correlated oxides as candidates for learning machines. The term "correlated" refers to the fact that electrons in such lattices strongly interact and the ground state is not what is predicted by classical band theory. Such materials can undergo insulator-metal transitions at near ambient conditions under external stimuli such as thermal or electrical fields, strain, and chemical doping. Depending on the mechanism driving the transition, intermediate states can be metastable with different volatilities, and the time scales of phase change can be controlled over many orders of magnitude. The change in electronic properties can be sharp or gradual, leading to digital or analog behavior. These properties enable the realization of artificial neurons and synapses and emulate the associative and non-associative learning characteristics found in various organisms. We examine microscopic properties concerning electronic and structural transitions leading to collective behavior and theoretical treatments of the ground state and dynamical response, showcasing VO₂ as a model system. Next, we briefly review algorithms designed from the plasticity demonstrated by phase changing systems. Finally, we conclude the brief review with suggestions for future research toward realizing non-von Neumann machines.« less

Functional interfaces between electronics and biological matter are essential to diverse fields including health sciences and bio-engineering. In this work, we report the discovery of spontaneous (no external energy input) hydrogen transfer from biological glucose reactions into SmNiO₃, an archetypal perovskite quantum material. The enzymatic oxidation of glucose is monitored down to ~5 × 10^⁻16 M concentration via hydrogen transfer to the nickelate lattice. The hydrogen atoms donate electrons to the Ni d orbital and induce electron localization through strong electron correlations. By enzyme specific modification, spontaneous transfer of hydrogen from the neurotransmitter dopamine can be monitored in physiological media.more » We then directly interface an acute mouse brain slice onto the nickelate devices and demonstrate measurement of neurotransmitter release upon electrical stimulation of the striatum region. These results open up avenues for use of emergent physics present in quantum materials in trace detection and conveyance of bio-matter, bio-chemical sciences, and brain-machine interfaces.« less

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO₃ films were grown with defectmore » densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO₃ bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO₃ films compared to their nonstoichiometric counterparts. Furthermore, this work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.« less

Requisite to growing stoichiometric perovskite thin films of the solid-solution A'_1-xA_xBO₃ by hybrid molecular beam epitaxy is understanding how the growth conditions interpolate between the end members A'BO₃ and ABO₃, which can be grown in a self-regulated fashion, but under different conditions. Using the example of La_1-xSr_xVO₃, the two-dimensional growth parameter space that is spanned by the flux of the metal-organic precursor vanadium oxytriisopropoxide and composition, x, was mapped out. The evolution of the adsorption-controlled growth window was obtained using a combination of X-ray diffraction, atomic force microscopy, reflection high-energy electron-diffraction (RHEED), and Rutherford backscattering spectroscopy. It is found thatmore » the stoichiometric growth conditions can be mapped out quickly with a single calibration sample using RHEED. Once stoichiometric conditions have been identified, the out-of-plane lattice parameter can be utilized to precisely determine the composition x. This strategy enables the identification of growth conditions that allow the deposition of stoichiometric perovskite oxide films with random A-site cation mixing, which is relevant to a large number of perovskite materials with interesting properties, e.g., high-temperature superconductivity and colossal magnetoresistance, that emerge in solid solution A'_1-xA_xBO₃.« less

Stoichiometric SrVO₃ thin films were grown over a range of cation fluxes on (001) (La_0.3Sr_0.7)(Al_0.65Ta_0.35)O₃ substrates using hybrid molecular beam epitaxy, where a thermal effusion cell was employed to generate a Sr flux and V was supplied using the metal-organic precursor vanadium oxytriisopropoxide (VTIP). By systematically varying the VTIP flux while keeping the Sr flux constant, a range of flux ratios were discovered in which the structural and electronic properties of the SrVO₃ films remained unaltered. The intrinsic film lattice parameter and residual resistivity were found to be the smallest inside the growth window, indicating the lowest defect concentration ofmore » the films, and rapidly increased for cation flux ratios deviating from ideal growth condition. Reflection high-energy electron diffraction showed that films grown within this range had smooth surfaces and diffraction patterns were free of additional spots, while otherwise the growing surface was rough and contained additional crystalline phases. Here, results show the existence of a SrVO₃ growth window at sufficiently high growth temperature, in which high-quality, stoichiometric films can be grown in a robust, highly reproducible manner that is invulnerable to unintentional flux variation.« less