The innovative objective of the TRINIDAD project is to extend to the microwave frequency range the concept of doped transmission used by optical telecommunication. A first aim is to develop within a 24 months period a loss-compensated spin-wave propagation medium. A second aim is to pattern this medium into a micron-size wave guide in order to achieve an analog delay line of unprecedented quality and integrable into the future electronics. The core idea of TRINIDAD is to join a magnetic insulator and a normal metal. In such a double-layered structure the magnetic insulator – Yttrium-Iron Garnet (YIG) – provides a low-loss propagation medium where an input microwave electromagnetic signal is converted into a slowly propagating spin-wave. A first key property of the targeted device is the use of ultra-thin films of YIG in order to reduce the group velocity of the spin-wave below 10m/s. A second key property is that intrinsic losses of the traveling spin-wave are partially or even fully compensated allowing the delay time to be increased beyond the natural spin-wave decay, which presently is a key issue that limits this technology. The oscillatory signal will be amplified by an injected flow of angular momentum (or pure spin current) from an out-of-equilibrium spin accumulation layer produced by the electrons moving in an adjacent metallic layer. The spin current will be created by the spin-Hall effect (requires strong spin-orbit metals or alloys: e.g. Pt, Ta or CuIr and AuW). The net result of the spin current will be to amplify (or to reduce, depending on the sign of the applied current) the propagating signal by the process of stimulated emission at the metal/insulator interface. Delays of few microseconds could then be potentially achieved over micrometer distances. In the future, such delay line could be used as the elementary building block for other high performance microwave devices such as an ultra-low phase noise oscillator or a voltage controlled tunable filter. Target applications lie in radar and telecommunication technology, which are looking for electronically tuned ultra-narrow band, non-reciprocal devices, combining both high-agility and ultra-narrow selectivity.

By setting a combination of advanced ultrafast optical approaches, SPINUP has for final objective the direct visualization and understanding of dynamical characteristics of sub-picosecond spincurrent pulses propagation at the nanoscale. The main methodology will be based on the direct spatially- (smaller than 30 nm) and time-resolved (shorter than 50 fs) measurements of pure spincurrents using advanced near-field non-linear optical microscopy and spectroscopy. Eventually, SPINUP would allow me to settle a novel field of expertise at CEA/SPEC, focused on time-resolved near-field optics to study the new trends of ultrafast magnetism. The scientific impact expected from this ANR JCJC “SPINUP” will be of utmost importance for the next generation of ultrafast spintronics devices and in a more general framework, for ultrafast nanoscience.

MIXES is a collaborative research project that explores the fundamental structural and electronic properties of novel 2D-0D nanomaterial, made of 2D materials in interaction with self-ordered nanoclusters grown using dry methods compatible with microelectronics industry processes. First results show that these nanomaterials, once implemented into tunnel junctions, demonstrate robust Coulomb blockade oscillations and magneto-Coulomb properties, preserved on device being 6 orders of magnitude larger than usual single-electron devices. These results have raised questions regarding the underlying fundamental physics that are addressed by this project. In particular, we will address the following fundamental questions: i) What is the chemical/structural/electronic nature of the 2D/0D interface? How are the local/extended structural and electronic properties of 2D/0D nanomaterials influenced by the nature of the 2D/0D interface, when it varies from van der Waals type to covalently bound ? (ii) What is the key mechanism behind many dissimilar nanoclusters apparently behaving as single or identical entities in the 2D-0D nanomaterial? How can it be mastered for simple and large-scale processing of a single electron device? iii) Can it be extended to other 2D materials such as dichalcogenic transition metals? iv) How can these properties be used to create new single electron multifunctional devices? We follow an interdisciplinary approach covering ab-initio modelling, surface science, structural analysis, nanofabrication and transport measurements. We keep as final goal to use these new knowledges to build novel architecture of multifunctional single-electron electronics and spintronics devices, operating up to room temperature.

RF signals are everywhere in today’s connected society. Surface Acoustic Wave (SAW) filters are widely used to distinguish between signals at different frequencies. Unfortunately, the performance of SAW filters drops above 5 GHz. Thin films of epitaxial LiNbO3 on sapphire host “guided” AW. These modes comply with the demand for higher frequency and higher efficiency. Unfortunately, despite the success of AW technology and its frequency progresses, two limitations remain inherent to AWs, specifically: (i) The absence of tunability once the geometry and material are defined. If several frequency bands are needed in an application, this requires several AW devices. (ii) The absence of non-reciprocity of acoustical wave propagation. In AW devices, the energy flows as easily in the forward and in the backward directions. The input of any AW device cannot be isolated from the influence of its output, as would be desirable for information processing purposes. Spin waves (SWs) are the eigenexcitations of the magnetization. They display rich linear and nonlinear physics and they offer the same miniaturization capability as acoustical waves. The dispersion relation of SWs can be engineered by material and geometry, and later adjusted finely by magnetic fields or spin-torque effects; Upon proper design, SWs can be strongly non-reciprocal, i.e. they propagate differently in opposite directions. The central hypothesis of our research is that coupling AWs with SWs is a route to overcome the intrinsic limitations plaguing acoustic wave technology: by researching at the interface between material science, magnetism, acoustics and microwave engineering, the objective of MAXSAW is to use specific features of spin-waves (SW) –tunability and non-reciprocity– to add new capabilities to state-of-the-art LiNbO3 AW-based filters. We will harness the ability to engineer the dispersion laws of both SW and guided AW to achieve tangential nesting of the propagation characteristics of AW and SW, i.e. match their frequency, wavevector, and group velocities. This last (novel) point, supplemented by the high confinement of the acoustical energy near the interface with the coupled spin-wave medium, ensures that even if the SW-AW coupling (i.e. the magneto-elasticity) is weak, truly magneto-elastic resonance with strong hybridized character can be harnessed and confer non-reciprocity and tunability to the wave propagating medium as well as to dedicated transducers. The end goal of MAXSAW is to demonstrate new rf components with unprecedented attributes: this includes adjustable delay lines, compact broadband isolators, and frequency-tunable filters all potentially perfectly adapted for 5G standards, that may offer valorization opportunities for us. To achieve its goals, MAXSAW comprises 4 technical work packages: WP1 defines the propagation medium for the hybrid waves by enhancing the magneto-elastic cooperativity. WP2 is devoted to the making of the propagation medium, including the acoustical materials growth and the customization of the magnetic materials. WP3 develops augmented transducers matched to the propagating medium to best benefit from the medium developments. Finally, the WP4 is the demonstration of novel rf devices that harness hybrid AW-SWs in the strong coupling regime. To demonstrate its objectives, the consortium shall build upon the expertise in state-of-the-art acoustic wave devices (FEMTO-ST, team of Pr. Bartasyte), spin-wave dynamics (C2N, team of Thibaut Devolder, coordinator), their mutual coupling (INSP, team of Laura Thevenard) and optimized non-reciprocal magnetic materials (CEA-SPEC, team of Grégoire de Loubens), complemented by the support of Frec|n|sys as industrial subcontractor.

One of the most promising features of topological matter is the presence of helical ballistic edge states, pure one-dimensional propagating electronic states protected from backscattering by spin-momentum locking. When coupled to superconducting electrodes, a supercurrent is carried by topological Andreev bound states (ABS) also presenting spin-momentum locking. However, we are still far from a complete understanding of the role of the spin degree of freedom and the parity conservation. A major issue is to find unambiguous experimental signatures of the topological protection. We propose to tackle this problem through measurements of the dynamics and relaxation mechanisms of such states, which is still poorly explored experimentally. Our general idea is to develop an ultrasensitive magnetic field sensor by combining cryogenic amplifiers adapted to giant magneto-resistive (GMR) sensors, both homemade. We plan to detect fluctuations of the supercurrent at equilibrium in topological material coupled to superconducting electrodes. These current fluctuations originate from thermal excitation of ABS on a time scale given by the inelastic relaxation time, which can be as large as few milliseconds. This makes possible the real time detection of supercurrent fluctuations. We thus propose to improve the bandwidth and sensitivity of GMR detector up to the MHz range in order to detect real time fluctuations of occupation of the topological ABS. We will use different topological materials (Bi nanowires, WTe2 and Bi4Br4) whose fabrication we master and on which we have evidenced edge states. Eventually, such a high sensitivity should allow us to detect persistent current created by 1D loops of helical edge states in topological systems without superconducting contacts. This would represent one of the most relevant and direct evidence of the topological states.