Evidence for chiral graviton modes in fractional quantum Hall liquids

Jiehui Liang; Ziyu Liu; Zihao Yang; Yuelei Huang; Ursula Wurstbauer; Cory R Dean; Ken W West; Loren N Pfeiffer; Lingjie Du; Aron Pinczuk

doi:10.1038/s41586-024-07201-w

Evidence for chiral graviton modes in fractional quantum Hall liquids

Nature. 2024 Apr;628(8006):78-83. doi: 10.1038/s41586-024-07201-w. Epub 2024 Mar 27.

Authors

Jiehui Liang^#¹, Ziyu Liu^#², Zihao Yang¹, Yuelei Huang¹, Ursula Wurstbauer³, Cory R Dean², Ken W West⁴, Loren N Pfeiffer⁴, Lingjie Du^{5

6}, Aron Pinczuk^{2

7}

Affiliations

¹ School of Physics, National Laboratory of Solid State Microstructures, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing, China.
² Department of Physics, Columbia University, New York, NY, USA.
³ Institute of Physics, University of Münster, Münster, Germany.
⁴ Department of Electrical Engineering, Princeton University, Princeton, NJ, USA.
⁵ School of Physics, National Laboratory of Solid State Microstructures, and Collaborative Innovation Center for Advanced Microstructures, Nanjing University, Nanjing, China. ljdu@nju.edu.cn.
⁶ Shishan Laboratory, Suzhou Campus of Nanjing University, Suzhou, China. ljdu@nju.edu.cn.
⁷ Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY, USA.

^# Contributed equally.

PMID: 38538799
DOI: 10.1038/s41586-024-07201-w

Abstract

Exotic physics could emerge from interplay between geometry and correlation. In fractional quantum Hall (FQH) states¹, novel collective excitations called chiral graviton modes (CGMs) are proposed as quanta of fluctuations of an internal quantum metric under a quantum geometry description^2-5. Such modes are condensed-matter analogues of gravitons that are hypothetical spin-2 bosons. They are characterized by polarized states with chirality^6-8 of +2 or -2, and energy gaps coinciding with the fundamental neutral collective excitations (namely, magnetorotons^9,10) in the long-wavelength limit. However, CGMs remain experimentally inaccessible. Here we observe chiral spin-2 long-wavelength magnetorotons using inelastic scattering of circularly polarized lights, providing strong evidence for CGMs in FQH liquids. At filling factor v = 1/3, a gapped mode identified as the long-wavelength magnetoroton emerges under a specific polarization scheme corresponding to angular momentum S = -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 modes have characteristic energies and sharp peaks with marked temperature and filling-factor dependence, corroborating the assignment of long-wavelength magnetorotons. The observations capture the essentials of CGMs and support the FQH geometrical description, paving the way to unveil rich physics of quantum metric effects in topological correlated systems.