The excitonic insulator – EI – is the heretic paradigm of condensed matter theory, a macroscopic quantum coherent state made of excitons, electron-hole pairs bound by Coulomb attraction, which spontaneously form and condense at thermodynamic equilibrium. Since excitons collectively enforce a many-body gap by sharing the same wave function, akin to Cooper pairs in the superconductor, the EI phase might display new, intriguing forms of macroscopic quantum coherence. So far, strong evidence was reported in bilayer systems only, as the spatial separation of electrons and holes simplifies the detection of the EI phase.
Here at Cnr-Nano Modena we hunt for the bulk excitonic insulator phase and its unique properties by investigating theoretically novel systems that sustain long-range electron-hole attraction. We focus on layered materials that exhibit huge excitonic effects, as a consequence of both reduced dimensionality and ineffective screening, and may host topological as well as other kinds of order. We work to build a self-contained, comprehensive theoretical framework of the EI that relies on the organic combination of state-of-the-art model and first-principles calculations. Our research team includes main developers of the Yambo code and operates within the larger framework of MAX – MAterials design at the eXascale, a European Centre of Excellence which enables materials modelling and simulations at the frontiers of High Performance Computing.