This assessment is based on version 1 of this paper. Version 2 is now available on arXiv — the authors may have revised their methods, results, or conclusions.
Visualizing orbital magnetism in electron doped rhombohedral multilayer graphene
Owen I. Sheekey, Trevor B. Arp, Benjamin A. Foutty, Ruoxi Zhang, Tixuan Tan, Ludwig F. W. Holleis, Yi Guo, Sandesh S. Kalantre
Abstract
Electron doped rhombohedral multilayer graphene at high displacement field features an exceptionally flat band minimum with near-ideal quantum geometry. Experiments in this regime observe the formation of a 'quarter metal,' in which the electron liquid condenses into a single spin- and valley flavor. Remarkably, recent experiments have found a zero resistance state in the same region of the density- and displacement-field-tuned parameter space, attributed to the formation of a chiral superconductor characterized by a finite-momentum Cooper pair condensate. Here, we use nanoSQUID-on-tip magnetometry to map the orbital magnetization of electron-doped rhombohedral graphene devices ranging in thickness between 3 and 13 layers. Magnetization within the quarter metal phases peaks at finite density, consistent with concentration of the Berry curvature in a finite-momentum 'ring of fire'. Correlating transport and local magnetometry data in a tetralayer sample reveals that the superconducting state has a finite orbital magnetic moment, providing direct evidence of its chiral nature. We further show that widely observed stochastic switching of the resistivity in the metallic regime arises from a density-tuned sign change in the valley-resolved total magnetic moment. This leads to the formation of metastable magnetic domains under typical gate control sequences and can also be harnessed for electric-field controlled switching of orbital moment across the entire device. Unexpectedly, we find magnetic inhomogeneity specific to the apparent normal state of the chiral superconductor, suggestive of a strain-tuned competition between magnetic and non-magnetic ground states. Our results point to a subtle energetic competition underlying the observation of chiral superconductivity in a narrow range of layer numbers.
AI Impact Assessments
(1 model)Scientific Impact Assessment
Core Contribution
This paper provides the first direct spatially-resolved measurements of orbital magnetization in electron-doped rhombohedral multilayer graphene (RMG), spanning 3 to 13 layers, using nanoSQUID-on-tip (nSOT) magnetometry. The work makes several interconnected discoveries: (1) experimental confirmation of the "Berry ring of fire" — a finite-momentum ring of concentrated Berry curvature — through the observation that magnetization peaks at finite carrier density rather than at the band edge; (2) direct evidence that the chiral superconducting state in tetralayer graphene possesses a finite orbital magnetic moment, confirming its time-reversal symmetry breaking nature; (3) real-space imaging of capacitively driven magnetic domain reversal, explaining ubiquitous stochastic switching phenomena in transport data; and (4) discovery of magnetic inhomogeneity in the parameter regime associated with chiral superconductivity in 6-layer graphene, suggesting strain-tuned competition between magnetic and non-magnetic ground states.
Methodological Rigor
The experimental approach is exceptionally thorough. The authors studied six distinct devices across five different layer numbers (3, 4, 5, 6, 13 layers), providing systematic cross-validation. The nSOT measurements are well-characterized, with detailed specifications for tip diameter (~240-350 nm), sensitivity (~2-4 nT/√Hz), scan height, applied fields, and temperature for every dataset. The careful distinction between differential magnetometry (δB) and quasi-DC magnetometry (ΔB) modalities, along with custom arbitrary waveform generation for domain stabilization, demonstrates sophisticated experimental control.
The theoretical framework employs self-consistent Hartree calculations with DIIS convergence acceleration, properly accounting for electrostatic screening — which becomes increasingly important for thicker multilayers. The decomposition of orbital magnetization into self-rotation and center-of-mass contributions provides clear physical interpretation. The comparison between calculated and measured magnetization profiles (Fig. 1) is convincing, with both showing the characteristic finite-density peak attributable to the Berry ring of fire.
One methodological subtlety handled carefully is the role of spin-orbit coupling in pinning spin moments out-of-plane even under large in-plane fields, which allows unambiguous identification of orbital ferromagnetism through easy-axis anisotropy. The temperature management around the nSOT — including documenting heating effects from the tip itself — adds credibility.
Potential Impact
Chiral superconductivity confirmation: The demonstration that the superconducting state carries finite orbital angular momentum is arguably the most impactful finding. Previous evidence for chiral superconductivity relied entirely on transport measurements, which cannot directly probe time-reversal symmetry breaking in a zero-resistance state. This magnetometric confirmation significantly strengthens the case for chiral superconductivity in RMG, a topic of intense current interest.
Reinterpretation of transport data: The real-space imaging of magnetic domains provides essential context for interpreting transport measurements across the field. The demonstration that stochastic resistivity switching arises from density-tuned sign changes in valley-resolved magnetization — creating metastable domains under typical gate sequences — has immediate implications for essentially all transport studies of quarter metals in RMG. The finding that transport currents themselves influence domain configurations (Fig. 3) is particularly important for experimental design.
Sample-to-sample variability: The observation of magnetic inhomogeneity specific to the chiral superconductor parameter regime in 6-layer graphene, where the device channel and contacts show different ground states, provides a concrete mechanism for understanding why chiral superconductivity appears in some samples but not others. The strain hypothesis is physically well-motivated and experimentally testable.
Electrically controlled magnetism: The first real-space imaging of capacitively driven magnetic reversal in metallic orbital ferromagnets, demonstrated across multiple layer numbers, establishes this as a generic phenomenon with potential applications in orbitronics.
Timeliness & Relevance
This work arrives at a critical moment. Chiral superconductivity in RMG was reported very recently (2025-2026), and the community urgently needs independent confirmation through probes beyond transport. The paper directly addresses the most pressing question: does the superconducting state actually break time-reversal symmetry? The systematic study across layer numbers also addresses the puzzling layer-number dependence of chiral superconductivity, which has emerged as a key theoretical challenge.
Strengths
Limitations
Overall Assessment
This is a high-impact experimental paper that provides the first direct magnetic imaging evidence for the chiral nature of the superconducting state in rhombohedral graphene, while simultaneously establishing a comprehensive picture of orbital magnetism across multiple layer numbers. The discovery of competing ground states in the chiral SC regime offers a compelling explanation for sample-to-sample variability and points toward strain engineering as a future direction. The work will be highly influential in the rapidly growing field of correlated electron physics in crystalline graphene systems.
Generated May 30, 2026
Comparison History (209)
Paper 2 offers higher potential impact by bridging fundamental topological physics with tangible real-world applications. While Paper 1 provides profound insights into chiral superconductivity, Paper 2 solves a major technological bottleneck: the all-electrical, zero-magnetic-field generation of skyrmion bags. Demonstrating this capability, alongside observations of complex 3D topological defects like magnetic monopoles, establishes a direct pathway to next-generation, low-power spintronic computing. This combination of fundamental discovery and immediate technological applicability gives Paper 2 exceptional timeliness, practical relevance, and broader impact across physics and engineering.
Paper 2 presents direct experimental evidence of chiral superconductivity in multilayer graphene using advanced nanoSQUID magnetometry, addressing a highly timely and competitive field. It resolves existing experimental mysteries like stochastic switching and provides critical insights into quantum geometry. In contrast, Paper 1 offers a phenomenological model for the well-established fractional quantum Hall effect but explicitly lacks derivations of fundamental properties like topological order or anyonic statistics, limiting its fundamental impact compared to Paper 2's breakthrough experimental findings.
Paper 2 demonstrates room-temperature nonlinear thermoelectric effects, bridging fundamental topological physics with practical applications in energy conversion and thermal management. While Paper 1 provides profound insights into chiral superconductivity in graphene, its findings are confined to cryogenic temperatures and specialized condensed matter subfields. Paper 2's room-temperature operation and lack of reliance on external magnetic fields give it broader cross-disciplinary impact across physics, materials science, and applied engineering.
Paper 1 likely has higher impact due to strong novelty and timeliness in moiré/flat-band graphene physics, providing direct real-space magnetometry evidence for chiral superconductivity and linking Berry-curvature-driven orbital magnetism to transport. The work is experimentally rigorous (nanoSQUID mapping correlated with transport), addresses widely observed phenomena (stochastic switching/domains), and can influence multiple areas (correlated electrons, topological superconductivity, quantum geometry, nanoscale magnetometry). Paper 2 is innovative for spintronics/nonlinear dynamics but is primarily theoretical and may have narrower near-term cross-field reach.
Paper 2 likely has higher impact: it reports direct experimental visualization of orbital magnetism in a timely, high-profile platform (rhombohedral multilayer graphene) tied to debated chiral superconductivity. The nanoSQUID magnetometry provides strong methodological rigor and a broadly useful capability, with immediate implications for correlated/topological superconductivity, Berry-curvature physics, and device-relevant electric-field control of orbital moments/domains. Paper 1 is novel and potentially transformative but is primarily theoretical/proposal-level and may face greater experimental integration risk and longer time-to-impact.
Paper 2 likely has higher impact because it provides direct real-space magnetometry evidence linking orbital magnetization, Berry-curvature physics, and chiral superconductivity (finite orbital moment) across multiple layer thicknesses. The combination of nanoSQUID imaging with correlated transport addresses an urgent, high-interest question (chiral superconductivity) with strong methodological rigor and clear experimental signatures, and it uncovers device-relevant phenomena (metastable domains, electric-field switching). Paper 1 is important for band-structure/quantum-geometry microscopics, but Paper 2 more directly advances and validates emergent phases with broader cross-field relevance.
Paper 1 introduces a broadly applicable theoretical framework bridging real-space experimental probes (STM) with momentum-space band topology. By establishing a new invariant based on wavefunction zeros, it offers a novel method to detect topological phases across diverse quantum materials, including TMDCs, Kagome metals, and twisted bilayer graphene. While Paper 2 provides critical experimental insights into chiral superconductivity in a specific graphene system, Paper 1's universal approach and theoretical innovation give it a higher potential for widespread foundational impact across condensed matter physics, fundamentally changing how researchers identify topological states.
Paper 2 provides direct experimental evidence for chiral superconductivity in rhombohedral graphene—a topic at the forefront of condensed matter physics with intense current interest. Its nanoSQUID imaging reveals fundamental insights into orbital magnetism, chiral pairing, and competing ground states, addressing major open questions. Paper 1 presents an elegant, well-executed sensor with practical magnetometry applications, but its incremental engineering advance has narrower impact than Paper 2's fundamental discoveries that could reshape understanding of unconventional superconductivity and quantum geometry.
Paper 2 provides direct experimental evidence for chiral superconductivity in rhombohedral graphene using cutting-edge nanoSQUID magnetometry, addressing one of the most timely and hotly debated questions in condensed matter physics. Its findings on finite-momentum Cooper pairing, orbital magnetism, and layer-dependent competition have profound implications for understanding unconventional superconductivity and quantum geometry. Paper 1 demonstrates an interesting neuromorphic application but relies on disorder-mediated mechanisms in a niche device context. Paper 2's fundamental insights, methodological sophistication, and relevance to a rapidly evolving field give it broader and deeper scientific impact.
Paper 2 likely has higher scientific impact due to its timeliness and breadth: it directly probes chiral superconductivity and orbital magnetism in rhombohedral multilayer graphene—an active, cross-disciplinary frontier spanning quantum materials, topology, superconductivity, and nanoscale magnetometry. The use of nanoSQUID imaging provides compelling, spatially resolved evidence (e.g., finite orbital moment of the superconducting state) and uncovers mechanisms behind resistivity switching and domain formation, with potential device applications (electric-field control of orbital moments). Paper 1 is rigorous and important for quantum Hall criticality, but its impact is more specialized.