Evidence of elusive high-energy chiral graviton excitations in quantum Hall systems
Electrons, negatively charged particles, sometimes coordinate their movements in ways that produce certain collective excitations referred to as quasiparticles. One case in which this occurs is the quantum Hall effect, a phenomenon that emerges when electrons are confined to a very thin layer, cooled to temperatures around 0 kelvin and exposed to a very strong magnetic field.
A framework called parton theory hypothesized the existence of emergent partons (i.e., quark-like quasiparticles in condensed matter physics that should not be confused with quarks and gluons in particle physics) to explain the collective excitations of quantum Hall states.
Recent geometric theoretical frameworks also suggest that small fluctuations in a system's quantum metric (i.e., a quantity describing the 'shape' of a quantum state) produce collective spin-2 excitations referred to as chiral gravitons.
In 2024, researchers at Nanjing University and other institutes set out to gather experimental evidence supporting the existence of chiral gravitons, which had so far proved difficult to observe.
Their most recent work, published in Nature Physics, reports the observation of multiple chiral gravitons, including one in the low-energy range and another in the high-energy range. This observation introduces a promising new approach for probing partons hidden in fractionalized quantum matter (i.e., systems in which particles appear to break down into smaller quasiparticles).
"In fractional quantum Hall (FQH) states around half filling, we observed only one kind of chiral graviton mode, now referred to as the low-energy graviton," Lingjie Du, senior author of the paper, told Phys.org.
"Later, around quarter filling, at filling factors such as v = 2/7 and 2/9, we observed a high-energy graviton in addition to the low-energy one. This finding is significant. Our earlier experimental work in 2024 indicated that the graviton energy is proportional to the fractional charge associated with an FQH state.
"Therefore, the observation of two graviton modes within one FQH state points to the presence of two distinct fractional charges, which can be naturally understood within the parton theory of the FQH effect."
Using chiral gravitons to detect emergent partons
In earlier studies, Du and his colleagues experimentally observed what is known as the low-energy graviton, yet they had not observed a high-energy one. Low-energy gravitons are quasiparticles emerging in the FQH effect that require less energy to emerge, while probing high-energy partons requires higher energy excitations.
Observing high-energy partons remained a key objective for the researchers, as it would offer more conclusive evidence supporting the so-called parton theory of the FQH effect.
"The partons discussed here are fractionally charged, quark-like quasiparticles, distinct from anyons, which can also carry fractional charge but obey anyonic statistics," Du explained.
"Fluctuations of the quantum metric can give rise to a long-wavelength spin-2 geometric excitation associated with high-energy partons, namely the high-energy graviton. In our new study, we used a method called circularly polarized resonant inelastic light scattering at ultra-low temperatures (around 50 mK) and in strong magnetic fields (up to 14 tesla) to probe the spin and energy of the graviton mode in the high-energy range, which enabled us to detect the high-energy graviton."
Essentially, the researchers studied two-dimensional (2D) electron gases in single quantum wells in which the FQH effect emerged at ultra-low temperatures and under strong magnetic fields. They did this using circularly polarized resonant inelastic light scattering, a technique that can reveal excitations inside a material.
The measurements collected by the team revealed the presence of both low-energy and high-energy gravitons. This ultimately allowed the team to shed light on the geometric excitations, providing spectroscopic evidence for the elusive high-energy partons, which had not been observed directly before this work. The result shows that the emergent partons are not merely mathematical constructs but quasiparticles with real geometric dynamics.
"The observation of multiple gravitons, particularly the high-energy graviton, is significant for validating the geometric theory of the FQH effect," Du said. "It also offers experimental evidence that FQH partons are bona fide quasiparticles in strongly correlated matter and provides long-sought evidence for the parton theory of the FQH effect."
A new window into fractionalized quantum Hall systems
This recent study introduces a promising new approach for detecting partons in quantum Hall systems, which relies on the collection of chiral graviton measurements. In the future, it could help improve existing theories of fractionalized matter, deepening the present understanding of various quantum materials and systems.
"Our experiments provide a route to resolving individual partons and their fractional quantum Hall phases through graviton measurements, which could be extended to a wide range of exotic phases of matter, including excitonic topological orders and fractional Chern insulators," Du said.
With their proposed methodology, the researchers have so far been able to detect specific collective excitations known as spin-2 chiral gravitons. In future studies, they would like to use a similar approach to observe more complex collective excitations in quantum matter.
"There are many interesting directions to explore," Du added. "For example, while the graviton modes we detected are chiral spin-2 modes, higher-spin modes, which may offer a possible connection to nonrelativistic string physics, could be detected using photons carrying orbital angular momentum.
"A superconducting instability arising from the pairing of neutral partons could give rise to a non-Abelian Moore-Read state, which could potentially be identified through the detection of graviton modes and is essential for topological quantum computation."
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Publication details
Zihao Yang et al, Emergent partons in fractional quantum Hall systems, Nature Physics (2026). DOI: 10.1038/s41567-026-03338-9.
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Citation: Evidence of elusive high-energy chiral graviton excitations in quantum Hall systems (2026, July 7) retrieved 14 July 2026 from https://phys.org/news/2026-07-evidence-elusive-high-energy-gravitons.html
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