New Frontiers in Emergent Materials

Fermi surfaces and electronic band structures paradigm occupy a central place in solid state science, since most of the physical properties of bulk metallic materials are governed by conduction electrons. The underlying hypothesis, which relies on a Bloch wave description of crystalline non-interacting electronic systems, is obviously not satisfied in numerous examples of emergent materials. The most challenging examples include strongly correlated electronic systems and structurally disordered materials showing spectacular macroscopic properties related with unconventional quantum order. Despite the inapplicability of the most common approaches to calculating electronic structure, the notion of electronic bands may often be generalized to describe most of these emergent materials. A standard example of such extension, from a phenomenological point of view, is the Fermi Liquid description of strongly correlated systems: despite strong interactions, low energy excitations can usually be described as the one of a non-interacting Fermi gas with renormalized effective mass. Experimentally, a large variety of techniques have also been developed initially from a Bloch wave description of electronic matter, including ARPES, quantum oscillations, Raman, X-ray or neutron scattering spectroscopies.

The present workshop aims at the experimental and theoretical studies of emergent materials such as heavy fermions, topological insulators, high temperature superconductors, or frustrated quantum magnets. The last decades have witnessed a flurry of activities in extending the frontiers of validity of the electronic band structure paradigm for describing and characterizing strongly correlated or disordered electron systems with unconventional phases. For example, modern mean-fields techniques have been developed to derive emergent effective non-interacting band models from strongly interacting systems. In order to model some spectroscopy experiments as well as thermodynamics and transport properties of emergent materials, localized magnetic degrees of freedom may be phenomenologically either fractionalized and included into an effective Fermisurface, or considered as bosonic/classical fields coupled to a Fermi liquid. For quantitative matching with experimental measurements, very powerful techniques have been developed, improving density functional theory methods in order to take into account relevant strong correlation effects, possible conventional and unconventional orderings, as well as time dependencies.

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