arXiv subjects

Paul Nizet

Publications and source records attributed to Paul Nizet.

5 recordsLinked to original sources

arXiv2026

Structure-driven analog optical control in ion-pumped SrFeO$_{3-δ}$ thin-film devices

Electrochromic devices (ECDs) offer a compelling route toward low-power, non-emissive optical modulators with nonvolatile states. However, their widespread implementation is hindered by limitations in operating voltage, switching speed, color tunability, and long-term stability. Mixed ionic-electronic conductors (MIECs) provide a promising alternative platform, enabling optical modulation through ion-driven redox and structural transformations. Oxygen-based MIECs offer enhanced durability, environmental robustness, and compatibility with oxide electronics and silicon photonics, yet remain largely underexplored for electrochromic and photonic applications. Here, we demonstrate structure-driven analog optical control in an ion-pumped SrFeO$_{3-δ}$ thin-film device by undergoing reversible oxygen-driven phase transitions between brownmillerite and perovskite structures. Phase transition is accompanied by pronounced changes in its electronic structure and optical constants. By harnessing these ion-induced structural transformations and integrating an optically passive Al$_2$O$_3$ interference layer, we achieve continuous and reversible modulation of optical transmittance and color. These results provide a general framework for ion-driven analog photonic and electrochromic devices and highlight the potential of oxygen-based MIECs for next-generation ionochromic systems compatible with silicon-based photonic platforms.

physics.app-ph↗

arXiv2024

Analog control of electrical conductivity in La0.5Sr0.5FeO3-δ through oxygen deficiency induced magnetic transition

Switchability of materials properties by applying controlled stimuli such as voltage pulses is an emerging field of study with applicability in adaptive and programmable devices like neuromorphic transistors or non-emissive smart displays. One of the most exciting approaches to modulate materials performance is mobile ion/vacancy insertion for inducing changes in relevant electrical, optical, or magnetic properties, among others. Unveiling the interplay between changes in the concentration of mobile defects (like oxygen vacancies) and functional properties in relevant materials represents a step forward for underpinning the emerging oxide iontronics discipline. In this work, electrochemical oxide-ion pumping cells were fabricated for an analog control of the oxygen stoichiometry in thin films of mixed ionic-electronic conductor La0.5Sr0.5FeO3-δ. We demonstrate over more than 4 orders of magnitude electronic conductivity control within the same crystallographic phase through the precise and continuous voltage control of the oxygen stoichiometry. We show that behind the modification of the transport properties of the material lays a paramagnetic-to-antiferromagnetic transition. We exploit such magnetoelectric coupling to show control over the exchange interaction between La0.5Sr0.5FeO3-δ and a ferromagnetic Co layer deposited on top.

cond-mat.mtrl-sci↗

arXiv2024

Solid-State Oxide-Ion Synaptic Transistor for Neuromorphic Computing

Neuromorphic hardware facilitates rapid and energy-efficient training and operation of neural network models for artificial intelligence. However, existing analog in-memory computing devices, like memristors, continue to face significant challenges that impede their commercialization. These challenges include high variability due to their stochastic nature. Microfabricated electrochemical synapses offer a promising approach by functioning as an analog programmable resistor based on deterministic ion-insertion mechanisms. Here, we developed an all-solid-state oxide-ion synaptic transistor employing $\text{Bi}_2\text{V}_{0.9}\text{Cu}_{0.1}\text{O}_{5.35}$ as a superior oxide-ion conductor electrolyte and $\text{La}_\text{0.5}\text{Sr}_\text{0.5}\text{F}\text{O}_\text{3-$δ$}$ as a variable resistance channel able to efficiently operate at temperatures compatible with conventional electronics. Our transistor exhibits essential synaptic behaviors such as long- and short-term potentiation, paired-pulse facilitation, and post-tetanic potentiation, mimicking fundamental properties of biological neural networks. Key criteria for efficient neuromorphic computing are satisfied, including excellent linear and symmetric synaptic plasticity, low energy consumption per programming pulse, and high endurance with minimal cycle-to-cycle variation. Integrated into an artificial neural network (ANN) simulation for handwritten digit recognition, the presented synaptic transistor achieved a 96% accuracy on the MNIST dataset, illustrating the effective implementation of our device in ANNs. These findings demonstrate the potential of oxide-ion based synaptic transistors for effective implementation in analog neuromorphic computing based on iontronics.

cs.ET↗

arXiv2024

Optoionic Impedance Spectroscopy (OIS): a model-less technique for in-situ electrochemical characterization of mixed ionic electronic conductors

Functional properties of mixed ionic electronic conductors (MIECs) can be radically modified by (de)insertion of mobile charged defects. A complete control of this dynamic behaviour has multiple applications in a myriad of fields including advanced computing, data processing, sensing or energy conversion. However, the effect of different MIECs state-of-charge is not fully understood yet and there is a lack of strategies for fully controlling the defect content in a material. In this work we present a model-less technique to characterize ionic defect concentration and ionic insertion kinetics in MIEC materials: Optoionic Impedance Spectroscopy (OIS). The proof of concept and advantages of OIS are demonstrated by studying the oxygen (de)insertion in thin films of hole-doped perovskite oxides. Ion migration into/out of the studied materials is achieved by the application of an electrochemical potential, achieving stable and reversible modification of its optical properties. By tracking the dynamic variation of optical properties depending on the gating conditions, OIS enables to extract electrochemical parameters involved in the electrochromic process. The results demonstrate the capability of the technique to effectively characterize the kinetics of single- and even multi- layer systems. The technique can be employed for studying underlying mechanisms of the response characteristics of MIEC-based devices.

physics.app-ph↗

arXiv2023

Intermodulation of optical frequency combs in a multimode optomechanical system

Phonons offer the possibility to connect the microwave and optical domains while being efficiently transduced with electronic and optical signals. Here, we present a multimodal optomechanical platform, consisting of a mechanical-optical-mechanical resonator configuration. The mechanical modes, with frequencies at 265 MHz and 6.8 GHz, can be simultaneously excited into a phonon lasing regime as supported by a stability analysis of the system. Both the MHz and the GHz modes enter a self-sustained oscillation regime, leading to the intermodulation of two frequency combs in the optical field. We characterize this platform experimentally, demonstrating previously unexplored dynamical regimes. These results suggest the possibility to control multiple mechanical degrees of freedom via a single optical mode, with implications in GHz phononic devices, signal processing, and optical comb sensing applications.

physics.optics↗