Pietro Bonetti - Harvard

Wednesday 19 Nov 2025, 08:00 → 19:15 US/Eastern

IAMM

 

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08:30 → 09:00 Pick up at hotel: Cristian Batista

Travel to IAMM.

09:00 → 10:00 Research Meeting

Cristian Batista

10:00 → 10:20 Talk Prep

10:20 → 11:20 Seminar: Searching for Experimental Signatures of Fractionalization

Zoom: https://tennessee.zoom.us/j/86292515289

In this talk, I will present some of my recent work which aims at understanding experimental observations in several strongly correlated platforms—cuprates, cold atomic simulators and organic compounds—in terms of exotic fractionalized states exhibiting topological order.

In the cuprates, the pseudogap phase shows multiple signatures of reconstruction of the large Fermi surface into four small hole pockets. In the absence of spontaneous symmetry breaking, this appears to contradict Luttinger’s theorem, which predicts that the volume enclosed by the Fermi surface remains constant. The resolution of this apparent contradiction lies in assuming that the pseudogap phase hosts fractionalized excitations with emergent gauge fields. I will show that these excitations are crucial not only for preserving Luttinger’s theorem but also for reproducing the Fermi surface topology observed in quantum oscillation measurements at low temperatures, where charge density wave order develops and further reconstructs the four hole pockets.

In the second part of the talk, I will discuss a recent experiment realizing a Hubbard model on a Lieb lattice in a cold atomic simulator [Lebrat et al., arXiv:2404.17555 (2024)]. At half-filling, a flat band was observed for zero Hubbard U, and a ferrimagnetic state for nonzero U, in agreement with theoretical predictions. In the presence of strong interactions, a new flat band was reported to emerge at quarter filling without symmetry breaking. Employing parton theories, we consider quantum fluctuations of several magnetic ground states identified using Hartree-Fock theory. We find a state with a flat band at the Fermi level coexisting with fractionalized bosonic spinon excitations carrying Z2​ gauge charges. This state represents a striking realization of doping-induced fractionalization.

If time permits, I will briefly review how ultrafast spectroscopic experiments in the cuprates and in the organic compound κ-(BEDT-TTF)2Cu2(CN)3​ can be interpreted in terms of fractionalized excitations.

References:
-P. Bonetti, M. Christos, S. Sachdev, PNAS 121 (50) e2418633121 (2024)
-A. Nikolaenko, P. Bonetti, A. Kale, M. Lebrat, M. Greiner, S. Sachdev, Phys. Rev. B 112, 045129 (2025)

11:30 → 12:00 Research Meeting

Speaker: Wonhee Ko (University of Tennessee, Knoxville)

12:00 → 14:00 Lunch

Yang

14:00 → 14:30 Research Meeting

Speaker: Prof. Adrian Del Maestro (University of Tennessee, Knoxville)

14:30 → 15:00 Research Meeting

Speaker: Joon Sue Lee (University of Tennessee, Knoxville)

15:00 → 15:30 Research Meeting

15:30 → 16:00 Research Meeting

16:00 → 16:30 Research Meeting

16:30 → 17:00 Research Meeting

17:45 → 19:15 Dinner