近日，南京大学的杜灵杰及其研究团队取得一项新进展。经过不懈努力，他们揭示分数量子霍尔液体中存在手性引力子模式的证据。相关研究成果已于2024年3月27日在国际权威学术期刊《自然》上发表。

本文利用圆偏振光的非弹性散射技术，成功观测到手性自旋-2长波磁光子，为分数量子霍尔（FQH）液体中存在手性引力子模式提供了确凿证据。特别地，在填充因子v=1/3的条件下，研究人员发现在特定偏振方案下，与角动量S=-2相对应的模式显现为长波磁子间隙模式，且此模式持续存在于极长波长范围。值得注意的是，该模式的手性特性在v=2/5时保持不变，而在v=2/3和3/5时则发生反转。

这些模式展现出特征能量和尖峰，并呈现出明显的温度依赖性和填充因子依赖性，进一步验证了长波长磁振子的分布。这些观测结果不仅揭示了手性引力子模式的本质，还验证了分数量子霍尔效应的几何描述，为深入探索拓扑关联系统中量子度量效应的丰富物理特性奠定了基础。

据悉，奇异的物理学可以从几何学和关联性之间的相互作用中产生。在分数量子霍尔(FQH)态中，人们提出了一种称为手性引力子模式(CGMs)的新型集体激发，作为量子几何描述下的内部量子度量的涨落量子。这种模式是引力子的凝聚态类似物，假设自旋为2的玻色子。它们的特征是手性为+2或2的极化态，能隙与长波极限的基本中性集体激发(即磁振子)一致。然而，CGMs在实验上仍然是不可实现的。

附：英文原文

Title: Evidence for chiral graviton modes in fractional quantum Hall liquids

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

Issue&Volume: 2024-03-27

Abstract: Exotic physics could emerge from interplay between geometry and correlation. In fractional quantum Hall (FQH) states, novel collective excitations called chiral graviton modes (CGMs) are proposed as quanta of fluctuations of an internal quantum metric under a quantum geometry description. Such modes are condensed-matter analogues of gravitons that are hypothetical spin-2 bosons. They are characterized by polarized states with chirality of +2 or 2, and energy gaps coinciding with the fundamental neutral collective excitations (namely, magnetorotons) 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.

DOI: 10.1038/s41586-024-07201-w

Source: https://www.nature.com/articles/s41586-024-07201-w