Quantum Hall Phenomena in Graphene Systems

Graphene’s two-dimensional honeycomb lattice endows charge carriers with massless Dirac character, leading to a half-integer quantum Hall effect and Landau level quantisation visible even at room temperature. The four-fold degeneracy of spin and valley degrees of freedom gives rise to a rich hierarchy of broken-symmetry states under high magnetic fields, in which electron–electron interactions open interaction-induced gaps at integer filling factors. Edge channels accompanying each quantum Hall plateau support dissipationless transport and reveal topological order, while fractional quantum Hall states in high-quality samples demonstrate strong correlations and anyonic excitations. Substrate alignment, moiré superlattices and electrostatic gating allow precise tuning of symmetry breaking, valley polarisation and collective excitations such as magnons and spin waves. These phenomena underpin resistance metrology and offer routes towards spintronic and quantum information applications, making graphene an archetypal platform for exploring both fundamental physics and emerging device architectures.

Research from Nature Portfolio

Recent studies have employed electrical noise spectroscopy to detect charge-neutral magnons in a symmetry-broken quantum Hall ferromagnet of the zeroth Landau level, revealing noise signatures above the Zeeman energy and identifying a ballistic magnon transport regime via edge-channel equilibration models. High-resolution atomic force microscopy has been used to spatially map broken-symmetry edge states in the zeroth Landau level, showing a gapped ground state bridging bulk and boundary and highlighting the interplay between moiré potentials and spin–valley symmetry breaking. Quantum-dot assisted tunnelling spectroscopy has resolved degeneracy-lifted Landau levels at high magnetic fields, tracking emerging spin- and valley-splits with steep field-dependence and minimised screening, thus illuminating symmetry-broken gaps in the graphene excitation spectrum.

Research from all publishers

Terahertz emission from electrically biased graphene Hall bars has been observed when the Hall voltage matches inter-Landau level spacing, indicating radiative N→0 transitions and pinpointing emission sites at current-contact corners with linewidths of order 10 meV. An all-electrical Fabry–Pérot cavity approach enabled excitation and detection of gapless spin waves in the E=0 Landau level of bilayer graphene, providing direct evidence of canted antiferromagnetic order and revealing high-velocity, coherent spin-wave propagation consistent with hydrodynamic theory. Theoretical work on graphene aligned with boron nitride has constructed phase diagrams of competing fractional quantum Hall states, predicting transitions from sublattice-polarised to Kekulé charge density wave and antiferromagnetic phases, and identifying novel canted valley-spin orders at selected filling fractions.

Quantum Hall Phenomena in Graphene Systems publication trend

The graph below shows the total number of articles in quantum hall phenomena in graphene systems across all publications each year (not limited to Nature Index journals).

Technical terms

Landau level: Discrete energy level of two-dimensional electrons under a perpendicular magnetic field.

Filling factor: Ratio of electron density to Landau level degeneracy, determining quantum Hall plateaus.

Edge state: One-dimensional conducting channel at sample boundaries in a quantum Hall regime.

Quantum Hall ferromagnetism: Spontaneous spin or valley polarisation arising in integer quantum Hall systems due to interactions.

Fractional quantum Hall state: Correlated electron phase at fractional filling factors supporting anyonic quasiparticles.

References

1. Electrical noise spectroscopy of magnons in a quantum Hall ferromagnet. Nature Communications (2024).
2. Edge channels of broken-symmetry quantum Hall states in graphene visualized by atomic force microscopy. Nature Communications (2021).
3. Quantum-dot assisted spectroscopy of degeneracy-lifted Landau levels in graphene. Nature Communications (2020).
4. Landau-level terahertz emission from electrically biased graphene. APL Photonics (2024).
5. Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet. Physical Review X (2021).
6. Theory of competing charge density wave, Kekulé, and antiferromagnetically ordered fractional quantum Hall states in graphene aligned with boron nitride. Physical Review B (2022).