Controlling strongly-correlated electronic states and inducing metal/insulator transitions by electric-field effect is the key objective of Mott-tronics (named after Nobel Prize laureate Sir Neville Mott). Conceptualized by IBM in the late 1990's, Mott transistors could surpass conventional MOSFETs in terms of ON/OFF ratios and power consumption. With ferroelectric gates, they could also lead to fast and high-endurance non volatile memories. Attempts to realize such devices have culminated with the recent report (Tokura’s group at Riken in Japan, Nature 2012) of a field-effect induced metal-insulator transition in VO2 thin films gated with ionic liquids. However, a subsequent study (Parkin’s group at IBM in the US, Science 2013) concluded that extrinsic, voltage-induced oxygen vacancy motion rather than intrinsic electrostatic effects was responsible for the large resistance change, raising controversy over such ionic liquid gated VO2 transistors. Two key challenges must be addressed to meet the long-standing goal in Mott-tronics of a non volatile, reversible, electronically-driven transition between a metallic and an insulating state: (i) identify a channel material in which a metal-insulator transition occurs at very low doping level; (ii) combine it with a switchable gate material capable of accumulating and depleting large carrier densities. FERROMON will address both challenges and investigate a model system consisting of epitaxial perovskite heterostructures combining a Mott insulator, (Ca,Ce)MnO3, with a (magnetic) ferroelectric, BiFeO3. BiFeO3/(Ca,Ce)MnO3 bilayers are of high crystalline quality and we recently demonstrated a large electrical response at room temperature induced by ferroelectric switching in both planar and vertical devices. The rich phase diagram of (Ca,Ce)MnO3 offers great potential for new exciting effects where ferroelectric field effect could not only drive metal/insulator but also magnetic phase transitions. In this framework, I will dedicate my 7-year experience with significant achievements in the field of oxide interfaces, nanoscale ferroelectrics, interface magnetoelectric coupling and ferroelectric devices to conduct the project with three main objectives: - Drive electronic and/or magnetic phase transitions in strongly correlated oxides by ferroelectric field effect - Understand at the atomic level the interplay between ferroelectricity and electronic properties at oxide interfaces - Exploit ferroelectric domain dynamics to control electronic and/or magnetic properties at the ns scale.

In 1986, the discovery of high-temperature superconductivity in cuprate-based compounds gave rise to an entirely new realm of research. Its unconventional superconductivity remains unexplained and during more than three decades, the researchers have searched for cuprates analogs. It was finally in 2019, when a group from Standford University reported superconductivity in hole doped layered nickelates compounds with a critical temperature of about 10-15 K. The superconducting phase shows the so-called infinite-layer structure (R1-x(Sr, Ca)xNiO2, R=Nd, Pr or La, x=dopant concentration), composed by two-dimensional NiO2 planes alternated with rare-earth (R) planes. Such phase is obtained from the parent perovskite (R1-x(Sr, Ca)xNiO3) phase, after selectively removing all the oxygen atoms at the apical sites of NiO6 octahedra. Similar to the cuprates, this impressive discovery initiated a new field of research, whose progress is now hampered by the great challenge of synthesizing these compounds. Thus, apart from the challenging synthesis of high-quality perovskite phase films, attaining the superconducting infinite-layer phase requires of a subsequent complex chemical topotactic reduction, which takes place inside a vacuum tube using CaH2 as a reducing agent. Such a method is highly impractical and prone to irreproducibility issues in between research groups and poor sample quality. Ultimately, it will never provide spatial resolution on the superconducting regions, which is a major technological barrier to implementing the use of superconducting nickelates in future nanodevices. OxyNicks project propose two innovative approaches to address the hurdles in the nickelates field: i) Enhance the control and reproducibility of the reduction process by depositing a reactive metal (Al, Y or Gd) using a magnetron sputtering. The metal will pump the oxygen from the perovskite phase during a redox reaction, becoming oxidized and transforming the film into the superconducting infinite-layer phase. Taking advantage of this new method, we will use angle-resolve photoelectron spectroscopy (ARPES) to visualize the electronic structure. Further, we will carry out magneto-transport and tunneling spectroscopy measurements to explore the uncharted physics underlying superconductivity in nickelates, barely explored so far due to the challenges in the synthesis. ii) The electrical control of the topotactic transformation in nickelates at nanoscale by means of the voltage generated with a biased atomic force microscopy (AFM) tip. The electric field created by the AFM tip will locally reduce the nickelate from the initial perovskite phase to the superconducting infinite-layer phase. This will provide us the necessary sub-micrometer control to fabricate the first prototypes of nanodevice using superconducting nickelates, namely Josephson junctions. Therefore, OxyNicks project aims at actively contributing to overcome the main barriers in the nascent field of nickelates, yielding new insights into the physics of these compounds and bringing nanoscale control of the superconductivity for the future incorporation of these materials into nanodevices.

Most spintronics devices are today based on the manipulation of spin currents that do not carry electrical charges but can be described as equal flows of electrons with opposite spins in opposite directions. The main operations in spintronics are the creation of spin currents from charge currents (electrical currents) and the detection of spin currents by transforming them into charge currents, in other words, conversions between charge and spin currents. Classical spintronics generally uses magnetic materials for these conversions, but it now appears that they can also be obtained by harnessing the spin-orbit coupling (SOC), the relativistic correction to the equation of quantum physics that can be significantly strong in materials containing heavy atoms. A new road for spintronics is now to explore how the spin-orbit interaction can be used as a tool to generate and detect spin currents. We recently demonstrated, using spin pumping and inverse spin Hall effect (Edelstein effect) experiments, a large efficiency of spin to charge current conversion (SCCC) in bi-dimensional systems. One is the Fe/Ge111 interface, involving Rashba and exchange splitting and the second one is the Alpha-Sn surface grown on InSb as a topological insulator surface. The mains objective of this proposal will be focused on: 1) The growth and control of these two dimensional surface states and their integration into spintronic devices. 2) The interfacial electronic states characterization and their spin properties from both experimental and theoretical aspects. 3) The final goal is to control the magnetization of a nanomagnet using 2D surface spin current and the resulting spin torque. More generally this relatively non explored spin momentum locked material can bring new tools for spintronics which aims to use the spin as a vector of information and communication. This project, should fill the gap between photoemission investigations and practical spintronic devices based on spin-orbit coupling. As a long-term vision for new technologies, the challenging goal of the project is to make one step forward in that field by demonstrating experimentally the writing of a nanomagnet by the absorption of pure spin currents generated and manipulated electrically in 2D materials. A switchable nanomagnet on spin helicity textured surfaces represents the first building block of magnetic data storage media, reprogrammable spin logics or even Spin Orbit Torque Oscillators. It is anticipated to work with low current and will contribute to low consumption devices. Moreover this experimental demonstration will be supported by theoretical works in order to give fundamental insight into the mechanisms of spin generation at surfaces and interfaces in both Rashba and topological insulator surface. It then addresses new paradigms based on quantum properties for spintronic component.

Ferroelectric (FE) materials that are characterized by a switchable polarization under application of an electric field have already attracted considerable interest for future electronic devices like memories because of their potential for fast switching capabilities, long retention time and high integration density. The ability of the FE polarization to tune the carrier density at the interface of an adjacent material has been recently used in FE-based tunnel junction (TJ) memories allowing a non-destructive readout of the information. Beyond that, the ability to tune continuously the polarization state and therefore the resistance through the FE barrier permitted to realize FE-based memristors mimicking biological synapses. This should therefore lead to a radically enhance of the computational power and energy efficiency of electronic devices. Alternatively, it has been also demonstrated very recently that using negative capacitance of a FE gate insulator in a FE-based Field Effect Transistor (FET), the so-called subthreshold swing which is limited to 60 mV/decade in classical FET can be subsequently reduced which in turn diminishes the power supply voltage and energy dissipation in the FET. It is worth to realize that the physical mechanism at the origin of the above mentioned effects is the FE instability/metastability (which is static in FTJs or transient in the negative capacitance response of FE-FETs). Interestingly, antiferroelectrics (AFEs), which are less studied materials especially as thin or ultrathin films, show also polar instability/metastability. Indeed, AFEs are very close in energy to FEs e.g. electric/elastic field can induce FE state from AFE one. However, AFEs have not, or scarcely, been considered in any memory or logic devices. Here in the framework of EXPAND project, we would like to explore the potential of AFEs in both TJs and FETs. In a AFE-based TJ, we aim at realizing a relaxation oscillator that emulates the behavior of a spiking neuron. Integrating this device into a RC circuit should thus allow building a spiking oscillator, whose spiking frequency can be adjusted by the voltage applied to the device. In AFE-based FETs, the energy landscape of the polarization which is at the origin of the negative capacitance is richer and therefore may not only significantly decrease the subthreshold swing but also generate novel logic functionalities such as dynamic hysteresis control. Reaching proof-of-concepts of such devices requires a better understanding of the fundamental and stability conditions of antiferroelectricity in thin films and a better knowledge of the interplay of AFEs with various interfaces including metal, dielectric, FE or another AFE layer. These heterostructures will then serve as building blocks for the design of a new nanoelectronic with expected boosted properties as well as innovative memory and logic devices. EXPAND is a multidisciplinary project requiring tight articulation between AFE-based film and heterostructure growth, precise structural and physical characterization with continuous feedback with modeling work to finally integrate them into prototype devices with improved performances and novel functionalities. Using AFE materials in innovative electronic devices will therefore lead to an improvement of Information Communication Technologies device performances, especially in term of power consumption and efficiency with storage and ultimate logic beyond C-MOS and more than Moore technologies.

SWAG is a multidisciplinary research project at the interface between spintronics, molecular electronics and electrochemistry for the controlled functionalization of surfaces. SWAG takes an original approach to push for the development of organic spintronics. The impermeable protection of ferromagnetic surfaces by graphene and the molecular functionalization of graphene constitute the two essential technological building blocks. This synergy made it possible for the first time to unlock a major technological barrier in the field of organic spintronics: the quality of interfaces. Beyond this essential aspect, this approach also makes it possible to implement new functionalities specific also to molecular systems valued for efficient spin transport such as quantum interference. New generation spintronics devices will be developed providing filtration efficiency of at least 80%.