Photo-induced phase transitions, driven by an intense optical pulse, allow for ultrafast control of the physical properties of materials by light (2 eV range). However, heat dissipation and temperature rise limit the control of coherent atomic motions and functions, therefore other means to drive materials with lower photon energy are required. In addition, the direct activation by light of soft lattice modes that drive phase transitions through lattice instability is not always possible, because of the optically inaccessible frequency range and/or because of the symmetry of the modes precluding optical transitions. Here we propose to explore the fascinating possibilities offered by Non-Linear Phononics (NLP) to control functional molecular materials. NLP takes advantage of strong infrared excitation (0.2 eV range) for driving a large amplitude high-frequency polar mode QIR, which can couple through nonlinear (anharmonic) terms and activate those "soft modes" able to drive phase transition. The time average creates an “effective” dynamic potential, rectifying the phonon field and adiabatically directing a slow mode, which may significantly change the average atomic positions to create a new phase of different structural and electronic orders. This process occurs abruptly, on the timescale of a phonon period. Ultimately, it appears possible to drive a symmetry breaking towards a more ordered state, allowing to revisit the old adage “structure makes function”. Up to now, this new opportunity is only just emerging, and has essentially been employed only on a few inorganic materials. In view of tantalising theoretical predictions, experimental opportunity, and the available technology suiting the challenge, we propose to develop nonlinear phononics for controlling electronic phase transitions in molecular materials. Importantly, the latter are rich resources of different functionalities. They present unique instabilities of molecular electronic states (charge, spin, …) that are strongly coupled to structural distortions of both the soft molecules and the soft lattice, and as such they are fitting test bed candidates for exploring NLP concepts in condensed matter. Our approach that consists in mixing experimental and theoretical expertise in material science seems an effective and attractive strategy in view of different types of coupling and different physical processes behind NLP driven phase transitions. ELECTROPHONE will benefit from the expertise of the different partners, as developing this challenging project will require detailed knowledge of crystalline structure, phonons and symmetry, theoretical calculations of intra- and inter-molecular modes, description of their couplings, as well as time-resolved experiments on the ultrafast time-scale. The ultimate goal of this project consists in recasting a new physical picture of Non-Linear Phononics in electronic phase transition materials by networking experimentalists and theorists.

Exchange statistics are related to the phase φ accumulated by the wavefunction describing the state of an ensemble of undistinguishable particles when two particles are exchanged. In the three-dimensional world, particles are divided between bosons, which obey φ=0 and tend to bunch together, and fermions, for which φ=π and which exclude each other via the Pauli exclusion principle. The situation is different in two-dimensional systems which allow the existence of quasiparticles called anyons with intermediate statistics between fermions and bosons, leading to intermediate degrees of bunching and exclusion. The strongly correlated phases of the fractional quantum Hall effect (FQH) have been predicted to host anyons carrying a fractional charge and obeying fractional statistics. The fractional charge has been observed twenty years ago by partitioning a beam of anyons and by measuring the resulting current noise, which is proportional to the fractional charge. However, despite numerous attempts, no direct signature of fractional statistics had been observed until two distinct experiments provided the first observations of fractional statistics this year. The first one performed by our consortium extended previous noise measurements in collider geometries to the FQH case in an anyon collider. Current noise measurements revealed the tendency of anyons to form larger charge packets in the collision process which is a signature of their intermediate exclusion statistics. The second experiment, performed by the Purdue group, observed braiding signatures in an anyon interferometer. Building upon this success, the project ANY-HALL aims at studying, experimentally and theoretically, the quantum statistics of anyons using the anyon collider as a test bench for fractional statistics. More precisely, the project will focus on the realization of three different objectives: The first objective of the project is to quantitatively study the fractional statistics of anyons for different topological orders. We will study anyon collisions for different filling factors (controlled by the magnetic field) corresponding to different FQH states with different statistics (and different values of the exchange phase φ). The second objective of the project is to understand the role of decoherence and relaxation on the experimental signatures of fractional statistics in the collider geometry. We will investigate the role of temperature and relaxation which are known to be important in the context of electron collisions. These effects, governed by the distance between the anyon emission and the central beam-splitter will be studied both experimentally and theoretically. The third objective of the project is the quantitative study of the dynamical regime. Anyon emission will be triggered by time-dependent drives in order to control the synchronization of the arrival times of anyons on the beam-splitter. We will also investigate how the number of anyons colliding on beam-splitter can be controlled by varying the amplitude of the current pulses. Our consortium is constructed such as to gather all the expertise necessary to tackle these questions. Experimentalists have the know-how to implement anyon collisions with state-of-the-art resolution. Specialists of sample growth and sample fabrication will fabricate high quality samples with good stability necessary for accurate noise measurements. Finally, theoreticians will provide the description of anyon collisions for complex edge channel structures, capturing the effects of relaxation and time-dependent drives.

The search for thermoelectric materials is an active topic, and promising new families such as chalcogenides have emerged in recent years with the figure of merit ZT reaching 1 or above. One of the possible tuning parameters of ZT in chalcogenides containing transition-metal cations is magnetism which can modify the transport parameters through a modification of the band structure and/or a modification of the entropy of the material. The thermal conductivity can also potentially be modified by magnetism. Even if promising interplay between thermoelectric properties and magnetism has already been demonstrated in some oxides and sulfides, a detailed understanding of these phenomena is still lacking. The aim of the project is to investigate the interplay between carriers, spins and phonons in three selected families of chalcogenides, guided by the input from Density Functional Theory (DFT). This will subsequently allow the optimization of the thermoelectric properties of these materials. The project will focus on three families of materials, the pentlandites, the pyrites and the thiospinels. Using these three different families, several parameters will be investigated. First in the case of pentlandites, the impact of a gradual introduction of magnetism in a Pauli metal and how the associated localization can contribute to an optimized power factor will be analyzed. For pyrites, the power factor is already very promising and several doping strategies will be followed to reduce the lattice part of the thermal conductivity. Finally, in thiospinels, DFT calculations will serve as a guide to define the best electronic and magnetic structures for optimizing the power factor and reducing the thermal conductivity. The project relies on a very close collaboration between DFT experts from CPHT and specialists in thermoelectric materials and magnetism in CRISMAT and GPM. A systematic screening of the thermoelectric properties of these materials will be performed by state of the art DFT calculations, and the transport properties of the most promising materials will be calculated, both for the electronic and phononic parts. The materials will be simultaneously synthesized, structurally characterized (both for chemical composition and possible disorder phenomena by x-Ray diffraction and transmission electron microscopy) and their thermoelectric properties measured in CRISMAT in a large range of temperatures (2K – 1000K) and up to 14T. Beyond studies of the magnetic properties by standard SQUID magnetometry, the magnetism will be investigated in GPM at the local scale by Mössbauer spectrometry, a powerful technique to probe magnetism and disorder and obtain crucial information about the magnetic characteristics such as oxidation state, spin configuration or magnetic moment direction at a given crystallographic site. The DFT calculations and experimental results will benefit from each other reciprocally throughout the project. This will allow us to define new pathways to optimize the figure of merit of these magnetic chalcogenides. This project fits perfectly in the ‘Sciences de base pour l’Energie’ committee as it will broaden the knowledge on how magnetism and spins can contribute to thermopower and thermal conductivity. It will help in the design of new thermoelectric materials, and will define original ways to tune the magnetic properties to optimize thermoelectric properties. These materials will have potential applications in the field of energy harvesting. The project will also shed more light on factors that affect thermal conductivity, a critical quantity in many energy applications, such as thermal barriers (small thermal conductivity) to reduce parasitic heat transfers or thermal management (with large thermal conductivity) for electronic devices.

One of the main goals of the experiments carried out at the CERN Large Hadron Collider is the study of new forms of hadronic matter, the quark-gluon plasma (QGP) and the color glass condensate (CGC), characterized by high parton density and strong non-linear phenomena. These forms of matter are also important for other high-energy experiments, like the electron-ion collider which is currently under project in both USA and at CERN, and also for understanding the evolution of the Early Universe. A good understanding of the fundamental theory of strong interactions, Quantum Chromodynamics (QCD), in the high-energy regime is mandatory in order to control the production and the properties of these new forms of matter. At high density, the QCD coupling is moderately weak, but naive perturbation theory nevertheless breaks down due to strong non-linearities: the relevant expansion parameter is the product of the coupling by the gluon occupation number, which can reach values of order one. A powerful strategy to circumvent this problem is to reorganize the perturbative expansion, by identifying and resumming to all orders the dominant effects of the interactions — i.e. those that are enhanced by the high-density effects. Within perturbative QCD at high energy, the most elaborate framework for performing these resummations is the CGC effective theory, that has been in particular introduced by members of the team and which is continuously evolving. Despite a lot of conceptual progress, the current status of the CGC effective theory is still unsatisfactory from the viewpoint of phenomenology. Its perturbative accuracy is still too crude to allow for realistic comparisons with data and the factorization schemes are not sufficiently developed, nor accurate enough, to deal with more exclusive final states, that are nevertheless measured in experiments. So far, all phenomenological applications of the CGC have departed from a rigorous first-principle approach by incorporating elements of modeling and ad-hoc free parameters in areas that should in principle be under perturbative control in QCD. In this project, our main goal is to develop the CGC effective theory to a level that allows reliable predictions and explicit comparisons with the phenomenology, without unnecessary modeling. This includes higher-order perturbative calculations, more sophisticated factorization schemes, and innovative numerical and analytical techniques. In particular, we plan to improve the accuracy of the CGC effective theory not only by including next-to-leading order perturbative corrections, but also by performing all-order resummations of special classes of radiative corrections, that are enhanced by 'collinear' logarithms. Albeit formally of higher order, such corrections are known to be numerically large and to lead to pathologies (like negative cross-sections) in fixed-order calculations. Members of our team have obtained important preliminary results on these resummations over the last months. Some of the cutting-edge problems that we intend to address include the calculation of single- and multiple-particle production in hadron-hadron collisions beyond leading order, the formation and thermalization of the quark-gluon plasma in ultrarelativistic nucleus-nucleus collisions, and the role of parton number fluctuations in hadron-hadron collisions. The members of the team have pioneering contributions on several among these topics. We also plan to compute less inclusive observables such as transverse spin asymmetries in high-energy collisions with polarized beams, and to elucidate some striking correlations, like the `ridge', that have been observed in multi-particle production in proton-proton and proton-nucleus collisions at the LHC.

Four-electron correlations will be induced in a Josephson bijunction formed by two junctions separated by a distance smaller than the coherence length. In addition to the usual Josephson effect in each junction, nonlocal Andreev processes between the junctions produce simultaneous transfer of two pairs (a nonlocal quartet), one in each side of the bijunction. The quartet current depends on the sum of the phases of the closeby junctions. This project aims at creating and detecting such nonlocal quartets by transport experiments, and extending the theoretical understanding as well as modelizing the experiments. The superconducting samples will have three current terminals and will involve either all-metallic junctions or tunable junctions made of carbon nanotube quantum dots. Both kinds of samples are already available or will be easily provided from previous experience with similar devices. The most striking prediction is the existence of a dc Josephson component due to quartets even in presence of voltage biases, provided both junctions are biased at opposite voltages. The detection of this dc quartet resonance will be achieved either by direct I(V) measurements or by Shapiro steps observation. A second set of experiments aims at detecting the dependence of the quartet current with the sum of the phases of the two junctions. This will involve generalizations of the usual SQUID for instance with two-loop circuits. All experiments will reveal the charge 4e of quartets. At last, a more exploratory topic is that of four-particle entanglement induced by quartet formation. The whole project relies on : i) a solid theoretical background; ii) existing samples; iii) existing experimental set-ups aimed at measuring three-terminal transport and the corresponding correlations. Promising results, both in theory and experiments, have been obtained in very preliminary studies, guaranteeing future observation of electron quartets in Josephson bijunctions. Beyond such experiments, generalization to arrays of Josephson junctions or mesoscopic grains open a vast field of research and potential applications, due to the nontrivial coupling of local phases, and the coexistence of dissipative and nondissipative currents, a new feature in superconductivity.