SIMIS Seminar on Field Theory and String Theory: Chiral graviton modes in quantum Hall liquids

Speaker: Lingjie Du (School of Physics Nanjing University, China)

Abstract: Gravitons are hypothetical neutral spin-2 bosons[1]. In the fractional quantum Hall (FQH) state at filling factor v = 1/3, a chiral graviton mode is predicted as quantum of metric fluctuations under a new quantum geometry description [2,3,4], which could be described by the corresponding Fierz-Pauli equation of gravitons [5]. Applicable to resembling FQH states, chiral gravitons are collective modes characterized by polarized states with chirality of +2 or -2, and energy gaps coinciding with fundamental excitations (i.e., magnetorotons) in the long-wavelength limit. However, such modes remain experimentally inaccessible. Here, for the first time, we observe chiral graviton modes in FQH liquids using inelastic scattering of circularly-polarized lights [6]. At v = 1/3, a sharp gapped mode identified as the long-wavelength magnetoroton, emerges under a specific polarization scheme corresponding to well-defined angular momentum -2, which persists at extremely-long wavelength. Remarkably, the mode chirality remains -2 at v = 2/5 but becomes the opposite at v = 2/3 and 3/5. The measurements of chiral spin-2 long-wavelength magnetorotons capture the essentials of the graviton modes. Our work paves the way to explore exotic phenomena arising from interplay of geometry and correlation, and offers access to quantum gravity in bench-top experiments.

Time: 16:00 ~ 17:00, Mon., Apr. 22, 2024

Location: Floor 6, Innovation Center Building 3, Weicheng Road 62, Yangpu District, Shanghai, China

Zoom Meeting No.: 423 317 8953
Password: SIMIS

Organizer: Sen Hu, Andrey Losev, Bong Lian, Wen-Jie Ma, Hao Zou

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