The magnetic properties of nanostructures have been intensely investigated in the last few years since it offers the opportunity to unfold new physical phenomena and design novel devices and applications all at once. An example of such simultaneous progress of fundamental understanding and practical developments can be found in the recent trend consisting in the electrical manipulation of magnetic properties. This opens the way to the design of spintronics devices in which the application of some magnetic field is no longer necessary. Up to now, the research on this topic has essentially focused on manipulating the magnetization of ferromagnetic nanostructures, yet some recent theoretical results suggest that it is also possible to control the magnetic ordering in antiferromagnets (AF) with an electric field or a current, in a more efficient way than for ferromagnets. Antiferromagnets would then play an active role, and not merely act as complementary layers in complex stacking as they do in present devices. The aim of the ELECTR-AF project is to explore the physical mechanisms underlying the electrical control of AF ordering. To unravel the intrinsic phenomena, we choose to focus on model systems. We will focus on heterostructures build around chromium epitaxial thin films, since the AF ordering of bulk Cr is both well known and easy to manipulate. Indeed, high quality chromium samples exhibit a spin density wave (SDW) ordering, the period of the modulated structure being incommensurate with the crystalline lattice. These model AF layers will be included in model heterostructures: we will grow epitaxial bcc metal/MgO/bcc metal trilayers (Cr being either the top or bottom metallic layer). This class of system has played a crucial role in the detailed understanding of spin-dependent tunnelling, and we will thus be able to build on the accumulated knowledge to explore the physics of spin polarized transport in antiferromagnets. We will first carry out thorough studies of the magnetic properties of Cr thin films and of the Cr/MgO interface, in order to obtain a detailed knowledge of our system. We will follow two distinct strategies to manipulate the magnetic ordering of Cr layers: - we will apply a voltage across an MgO layer in order to accumulate charges at the Cr/MgO interface. Given the large sensitivity of Cr to doping, we expect to modify the SDW period. - we will flow a spin polarized current through a Cr layer. We expect to observe spin transfer torque effects, and thus induce switching or precession of Cr ordering parameter. To observe the evolution of Cr magnetic ordering with the external perturbation, we will combine diffraction and magnetotransport measurements. One challenge of this project is to obtain information on the elusive magnetic ordering of Cr. Neutron diffraction is the ideal tool to do so, since it gave direct access to the properties of the SDW (direction of propagation, period, polarization). This project will give us the impetus to push the limits of the technique. We will also use synchrotron-based techniques and benefit from the latest developments in terms of electronic microscopy. The experimental aspects of this project are thus highly ambitious, but we are plainly confident these challenging experiments can be done, in the light of feasibility tests we have run and recent developments in the different techniques.

The race to room temperature superconductivity never ceased to be in full swing since its discovery in 1911. This fascinating phenomenon, where the material loses its resistivity to current flow below a critical temperature (Tc), stands out as a solution to societal challenges relevant to energy, transport, health and computation fields and is already at play in several modern infrastructures. At the current state of the art, the highest critical temperatures at ambient pressure were found to be achieved in a class of copper oxide based materials discovered in 1986, namely cuprates. The pristine cuprate materials are antiferromagnetic Mott insulators where hole doping induces a superconducting state that survives, in best cases, up to 135K, above the liquid nitrogen temperature. Over the years, cuprate superconductors have shaken the scientific community. They have proven to be an inexhaustible well of exotic electronic instabilities that stimulated a wide range of deep experimental and theoretical investigations that lay at the heart of modern condensed matter physics. The electronic phase diagram of hole-doped high-Tc superconducting cuprates is dominated by the enigmatic pseudogap phase, overhanging the superconducting dome in the underdoped regime. The pseudogap state is believed to be a key issue towards the understanding of the superconducting mechanism, either playing the role of a preemptive state for superconductivity, or of an order parameter characterized by broken symmetries that instead competes with superconductivity. Despite decades of intense experimental and theoretical efforts, the origin of this mysterious electronic state of matter remains a puzzle. A multitude of experimental probes demonstrate discrete time reversal, parity, and rotation symmetry breakings occurring concomitantly with the establishment of the pseudogap, interpreted as the hallmarks of a hidden magnetic order preserving the lattice translational symmetry (q=0 magnetism). While classical interpretations in terms of spin or orbital magnetism fail to reproduce the experimental results, exotic phases involving quantum magneto-electric loop currents offer a satisfying description of the underlying electronic states leading to such a q=0 magnetism. Since this magnetism however preserves the lattice translational symmetry, none of its related broken discrete symmetries can induce the needed gap. Recently, we discovered novel magnetic correlations in the pseudogap phase, giving rise to magnetic scattering at q=1/2 in reciprocal space that could change the deal. Together with the q=0 magnetism, such correlations yield a hidden magnetic texture, within the CuO2 unit cells, that breaks the lattice translational symmetry and may play a role in the pseudogap opening. The NEXUS project follows a two-pronged transdisciplinary approach, connecting condensed matter chemistry and physics. The two main objectives of this project are : i) probing the universality of the q=1/2 magnetism in the pseudogap phase of different cuprates families, its characterization (as a function of doping, temperature, magnetic field) and understanding its interplay with other electronic instabilities within the pseudogap state such as the charge density wave and superconductivity and ii) Investigating the signatures of lattice translational symmetry breaking in the pseudogap state, arising from the hidden loop current magnetic texture, that would be the direct proof of the link between the loop current magnetism and occurrence of the pseudogap. The methodology of NEXUS includes an important solid-state chemistry and crystal growth activity of various cuprates using the travelling solvent floating technique and the self-flux method. The investigations of the new q=1/2 magnetic correlations and their connection with the q=0 magnetism in the different cuprates will be carried using state of the art neutron scattering and resonant X-ray diffraction on large-scale facilities.

The project NirvAna aims to evidence anapoles (or polar toroidic dipoles) in condensed matter physics and more particularly in high temperature copper oxide superconductors. A spontaneous circulating loop current state, belonging to the anapole class, has been proposed to be the driving force controlling the physics of these materials. Using polarized neutron diffraction, we have already discovered a novel magnetic state in their most mysterious electronic state, the so-called “pseudo-gap phase”. It is broadly debated among the community that understanding the origin of the “pseudo-gap phase” would uncover the mystery of the high temperature superconductivity in copper oxide materials. We wish now to study whether the observed order corresponds to the orbital magnetic moments generated by the spontaneous microscopic loop currents described above. We propose to build an accurate polarized neutron diffraction setup: we will be able to perform experiments to resolve the magnetic structure factor of the novel magnetic order in various cuprates to highlight these anapoles. The project will also address the fundamental issue of the mechanism of high-temperature superconductivity of copper oxides, which remains so far still unsolved. Indeed, it is argued that superconductivity would emerge from such a novel state where associated low energy fluctuations will provide the glue for Cooper superconducting pairs. We propose to develop more powerful inelastic polarized neutron scattering measurements to evidence the quantum critical fluctuations, responsible in this approach for the high temperature superconductivity. The NirvAna project will identify anapoles in condensed matter as well as a novel mechanism for high temperature superconductivity. A final outcome of this proposal is to find out other systems with strong electronic correlations where similar novel electronic states might occur.

Alternate coolants are needed to replace the use of increasingly scarce liquid helium, required, for instance, to cool the superconducting magnets used in medical resonance imaging. Magnetocaloric materials, with their entropically driven cooling power when cycled in a magnetic field, are such a replacement. The gadolinium-based garnets developed recently show amongst the largest magnetocaloric effects ; yet the cooling power of those materials peaks below 2 K, too low for many applications of liquid helium. The aim of the SAKÉ project is to find new rare-earth garnets with better magnetocaloric performances, by adequate substitutions on the three available cationic sites of the garnet structure. The project originality is the investigation of high-entropy garnet oxides to achieve this goal. Moreover, the chosen consortium offers an unmatched expertise in neutron scattering techniques, which will be a key asset to correlate chemical substitutions with changes in magnetic anisotropy and ground states in applied magnetic field, for an in-depth understanding of the key parameters controlling the magnetocaloric effect.

Lubricating oils are being increasingly used across several industrial applications and the demand for these materials is on the rise and is expected to grow further in order to reduce machinery energy consumption and wear. Within this framework, the development of high performance lubricants is the key for the expansion of important industries and markets. Recently ionic liquids (ILs) have been shown to be promising candidates for novel high performances lubricants thanks to their various physico-chemical properties and their ability to lower significantly the friction between two surfaces. Such promising properties of ILs were found to be highly related to their capacity to nanostructure in bulk and at interfaces. However, the range of viscosities available in most IL classes is rather narrow compared to macromolecular lubricants. Poly(ionic liquid)s (PILs) are thus promising candidates to translate the frictional and chemical properties of both polymers and ILs to innovative and highly tuneable macromolecular lubricants. The addition of local interactions inherited from ILs to macromolecules results in a complex and rich panel of chemical and physical properties opening new opportunities to design polymeric materials with targeted functions which are highly related to both structural and dynamical properties of PILs. The POILLU project aims to take advantage of the lubrication properties of ILs and strong slippage ability of polymer melts to develop PILs with enhanced lubrication properties. Supported by the synthesis of a new class of tailored PILs specifically designed to meet the stringent criteria and ambitious objectives of this the project, this multidisciplinary consortium will perform a detailed molecular description of the bulk and interfacial stress transmission mechanisms involved in PILs using complementary state-of-the-art experimental techniques mastered by skilled soft matter physicists. The coupling of extensive bulk rheological characterization and advanced scattering techniques (SANS, WAXS) will enable us to determine the multi-scale structure/dynamic relationship occurring in PILs. The enhanced interfacial nano-structuration of PILs and its impact on surface chains dynamics will be studied thanks to Grazing Incident X-ray Scattering and Surface Force Apparatus nano-rheological measurements. Finally, the lubrication properties of PILs will be characterized using photobleaching based velocimetry technique. This interdisciplinary approach gathering internationally renowned skills in polymer chemistry, physical chemistry and physics that will highlight the exotic properties of PILs both in bulk and at interfaces opening appealing scientific perspectives in the field of complex polymeric materials targeting specific function through a multiscale molecular design.