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TT: Fachverband Tiefe Temperaturen

TT 4: Topological Insulators

TT 4.13: Vortrag

Montag, 17. März 2025, 12:45–13:00, H33

Exciton condensation driven by bound states of Green's function zeros — •Ivan Pasqua, Andrea Blason, and Michele Fabrizio — International School for Advanced Studies (SISSA), Via Bonomea 265, I-34136 Trieste, Italy

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. The analysis of the zeros offers a new perspective on the increasingly studied topic of excitonic insulators (EI), typically understood as the condensation of bound states between the valence and conduction bands of poles of the Green's function. Indeed this picture appears paradoxical in Mott insulators (MI), where the large gap between the Hubbard bands seemingly precludes the formation of such bound states. Yet, a continuous transition from a MI and an EI is observed in the Bernevig-Hughes-Zhang model using the dynamical cluster approximation. We find that a nontopological EI intrudes between the QSH and MI regimes. Our analysis suggests that excitons in the MI, which soften at the transition to the EI, could be bound states between valence and conduction bands of Green's function zeros. Our work proposes a novel mechanism for exciton condensation and highlights the role of Green's function zeros in diagnosing the properties of correlated phase of matter.

Keywords: Excitons; Mott insulators; Green's function zeros; Topological insulators; Fractionalized excitations