The guiding principle of our research is the quest for new magnetic phases of matter. In this respect, magnetic frustration, stemming either from the geometry of the lattice (see Fig. 1), or from competition between different kinds of magnetic interactions, may lead to very wide range of exotic phenomena and magnetic states, that can be ordered (ex. non-collinear, chiral) or disordered (ex. spin liquid, spin ices, where the competing interactions prevents the system from conventional magnetic ordering).
Understanding, characterizing and classifying this novel states of matter, having non-trivial static and dynamical correlations, is one of the main goal of the current research in frustrated systems : degeneracy of the ground-state ? broken symmetry and underlying order parameter (nematic order, topological order, etc.) ? range of spin-pair correlations (short- vs long-ranged) ? elementary excitations (local soft modes, fractional bosonic excitations such as spinons and “magnetic monopoles”, excited states associated to defects, etc.) ? We also study materials prone to magnetic frustration in which there is additional competition/cooperation between several degrees of freedom (spin, orbit, lattice, charge) and or additional ingredients such as strong spin-orbit coupling (e.g. in iridates).
Experimentally, answering these questions requires a combination of complementary probes developed at the Néel Institute or based on large scale facilities : magnetometry, neutron and X-ray scattering under extreme conditions (very low temperatures, high magnetic fields). Using these techniques, we mainly focus our attention on classical and quantum properties of lattices based on corner-sharing triangles or tetraedra or other geometries (pentagons). The experimental results are confronted to models in a fructuous comings and goings through collaborations with theoreticians. This activity is also based on the use of high quality materials, in particular single-crystals, and therefore relies on a synthesis work realized inside or outside the laboratory.
Members of the team