Ivan Pasqua

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The spectral properties of electronic systems are encoded in the single-particle Green’s function, with theoretical efforts traditionally focusing on the position and nature of its poles. Only recently, Green’s function zeros have been recognized as important hallmarks of non-symmetry breaking strongly correlated insulators and, possibly, of fractionalized excitations, challenging the conventional understanding of quasiparticles.

In this seminar, I will discuss how the Landau’s theory of Fermi liquids can be extended to encompass a broader class of interacting systems [1]. I will then illustrate how this new perspective sheds light on two case studies [2, 3].

The first case study concerns the increasingly studied topic of excitons in strongly correlated insulators, e.g. Mott insulators (MI). In MI the large gap between the Hubbard bands seemingly precludes the formation of bound states that could condensate in an excitonic insulator, as instead observed in numerical studies.

The second case focuses on the intriguing dichotomy that has been observed in the topological Kondo insulators SmB6 and YbB12. These materials display metallic thermal properties and insulating electrical
behavior, as if they hosted quasiparticles carrying entropy but not charge. Experiments also suggest the presence of well-defined Fermi surfaces, despite the insulating gap.

Our work, supported by numerical simulations within the dynamical cluster approximation, demonstrates how the zeros provide a unified picture, reconciling the apparently paradoxical behaviors emerging in the two case studies.

[1] M. Fabrizio, Nature Communications 13, 1561 (2022)
[2] I. Pasqua, A. Blason, M. Fabrizio PRB 110, 125144 (2024)
[3] A. Blason, I. Pasqua, M. Ferrero, M. Fabrizio PRB 110, 235115
(2024)

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SISSA
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Contact: Karim Chahine