The project has proceeded in many directions bringing about several results. I will herein present what I repute the main ones.
1. We have proposed [1] that the photoinduced superconductivity observed in K3C60 realizes a novel laser cooling mechanism made possible by the dual nature, partly metallic and partly insulating, of the correlated molecular conductor K3C60. Our transient cooling mechanism is quite general, as we discuss in [2] and pictorially explained in Fig. 1, and it might be realized in other correlated metals, too. It is sufficient that the metal hosts localized excitations, which can serve as entropy sink when the laser is on, and which very gradually release back that entropy when the laser is off.
2. Upon lowering temperature, V2O3 undergoes a first order transition from a rhombohedral corundum metal into a monoclinic antiferromagnetic Mott insulator. The structural transition is martensitic and leads to the coexistence of monoclinic twins. It is therefore worth exploring the entangled dynamics of electronic and structural degrees of freedom across the transition. Our experimental colleagues designed a nice experiment to detect through the dichroic signal of photoemission microscopy the real space dynamic of monoclinic and corundum domains by increasing T or by photoexciting the sample. At the meantime, we built a Landau-Ginzburg free-energy functional that describes both the shear strain driving the structural transition and the electronic parameter distinguishing the metal from the insulator. This functional reproduces well the experimental evidence and suggests that the presence of domains can be exploited to gain full control of the insulator-metal transition in V2O3, see Ref. [3] and Fig. 2.
3. Small-angle twisted bilayer graphene form a moiré superstructure with a cell containing tens of thousand of C atoms. We found that the normal modes of the superlattice include very special ones, almost nondispersive and modulated on the large supercell length scale, see Fig.3 and Ref. [4]. These modes were found to be extremely efficient in breaking the emergent valley symmetry leading to topological insulating phases, see Fig. 4 and Ref. [5], not in disagreement with those observed experimentally.
4. There is evidence in several Mott insulators of quasiparticle excitations like those of metals, and great interest in spinon Fermi surfaces within spin-liquid insulators. We have shown in Refs. [6] that these properties are consistent with Landau’s Fermi liquids within the Luttinger surface scenario, which can also explain the existence of quantum oscillations in insulators.
[1] Cooling quasiparticles in A3C60 fullerides by excitonic mid-infrared absorption, A. Nava, C. Giannetti, A. Georges, E. Tosatti and M. Fabrizio, Nature Physics 14, 154 (2018).
[2] Selective transient cooling by impulse perturbations in a simple toy model, M. Fabrizio, Physical Review Letters 120, 22061 (2018).
[3] Nanoscale self-organization and metastable non-thermal metallicity in Mott insulators, A. Ronchi et. al, Nature Communications 13, 3730 (2022).
[4] Valley Jahn-Teller effect in twisted bilayer graphene, M. Angeli, E. Tosatti, and M. Fabrizio, Physical Review X 9, 041010 (2019).
[5] Local Kekulé distortion turns twisted bilayer graphene into topological Mott insulators and superconductors, A. Blason and M. Fabrizio, Physical Review B 106, 235112 (2022).
[6] Emergent quasiparticles at Luttinger surfaces, M. Fabrizio, Nature Communications 13, 1561 (2022); Spin liquid insulators can be Fermi liquids, M. Fabrizio, Physical Review Letters 130, 156702 (2023).
