BEGIN:VCALENDAR VERSION:2.0 CALSCALE:GREGORIAN PRODID:UW-Madison-Physics-Events BEGIN:VEVENT SEQUENCE:0 UID:UW-Physics-Event-9478 DTSTART:20251106T160000Z DURATION:PT1H0M0S DTSTAMP:20260405T165750Z LAST-MODIFIED:20251024T143602Z LOCATION:5310 Chamberlin SUMMARY:Searching for Experimental Signatures of Fractionalization\, R . G. Herb Condensed Matter Seminar\, Pietro Bonetti\, Harvard DESCRIPTION:In this talk\, I will present some of my recent work which aims at understanding experimental observations in several strongly c orrelated platforms—cuprates\, cold atomic simulators and organic co mpounds—in terms of exotic fractionalized states exhibiting topologi cal order.
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\nIn the cuprates\, the pseudogap phase shows mult iple 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 tha t the volume enclosed by the Fermi surface remains constant. The resol ution of this apparent contradiction lies in assuming that the pseudog ap 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 topo logy observed in quantum oscillation measurements at low temperatures\ , where charge density wave order develops and further reconstructs th e four hole pockets.
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\nIn the second part of the talk\, I wil l discuss a recent experiment realizing a Hubbard model on a Lieb latt ice in a cold atomic simulator [Lebrat et al.\, arXiv:2404.17555 (2024 )]. At half-filling\, a flat band was observed for zero Hubbard U\, an d 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. E mploying 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 fractional ized bosonic spinon excitations carrying Z2​ gauge charges. This sta te represents a striking realization of doping-induced fractionalizati on.
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\nIf time permits\, I will briefly review how ultrafast s pectroscopic experiments in the cuprates and in the organic compound Î º-(BEDT-TTF)2Cu2(CN)3​ can be interpreted in terms of fractionalized excitations. URL:https://www.physics.wisc.edu/events/?id=9478 END:VEVENT END:VCALENDAR