Two superconducting-like states were observed near a band inversion. Both were confined to regions where electron and hole Fermi surfaces coexist, a restriction that is consistent with a possible dual-carrier origin for superconductivity. The observation suggests that the presence of both carrier types may be relevant to the superconducting phases, but the reported results do not establish the microscopic pairing mechanism.

The experiments also identified a ferroelectric orbital magnetic state with a sharply switchable magnetic response. Its magnetism reverses under a unipolar electric field, and the magnetic hysteresis is itself reversible by the electric field. This behavior is consistent with a phenomenological model of coupled electric and magnetic polarization.

Unlike previously reported multiferroicity near zero electric field, the newly identified state switches under a unipolar field, which the authors interpret as a signal of spontaneous electric polarization. The observations therefore link an orbital magnetic order with an electrically switchable ferroelectric response, rather than merely showing that magnetic and electric properties occur in the same sample. Overall, the study expands the experimental phase map of rhombohedral graphene into an overlapping-band semimetallic regime.

It demonstrates that this regime can accommodate correlated insulating behavior, multiple superconducting-like pockets and two separate multiferroic orbital magnetic orders. The possible connection between electron and hole Fermi surfaces and superconductivity remains a mechanistic question, while the evidence for spontaneous electric polarization comes from field-reversible magnetic switching and its consistency with the coupled-polarization model. Together, the results identify rhombohedral hexalayer graphene as a platform in which superconductivity, orbital magnetism and ferroelectric behavior can be investigated within the same correlated semimetal, although the preview does not provide the full experimental details needed to assess those phases in greater depth.

Subject of Research: Experimental mapping of superconductivity and ferroelectric orbital magnetism in semimetallic rhombohedral hexalayer graphene

Article Title: Superconductivity and ferroelectric orbital magnetism in semimetallic rhombohedral hexalayer graphene

Article References: Deng, J., Xie, J., Li, H., Taniguchi, T., Watanabe, K., Shan, J., Mak, K. F., & Liu, X. (2026). Superconductivity and ferroelectric orbital magnetism in semimetallic rhombohedral hexalayer graphene. Nature Physics. https://doi.org/10.1038/s41567-026-03443-9

Image Credits: AI Generated

DOI: 10.1038/s41567-026-03443-9

Keywords: rhombohedral graphene, hexalayer graphene, semimetal, superconductivity, orbital magnetism, ferroelectricity, multiferroicity, band inversion, quantum phases, correlated electrons, ferroelectric, orbital

The problem with copper is fundamental to the physics of charge transport at small scales. In a bulk metal, electrons travel long distances before scattering off imperfections, giving copper its famously low resistivity of about 1.7 micro-ohm centimetres. But when a wire’s dimensions approach the mean free path of its electrons, two effects conspire to raise resistance dramatically. Electrons begin to scatter off the surfaces and grain boundaries of the wire, and the effective cross-section available for conduction shrinks. In state-of-the-art copper interconnects, which in the most advanced chips have critical dimensions below 20 nanometres, this size effect causes resistivity to soar, producing signal delays, wasted power and degraded reliability. As the semiconductor industry pushes toward ever-denser circuitry, the wires that tie transistors together have become a limiting factor in computing performance.

The Hong Kong Polytechnic University team, together with collaborators at South China Normal University, The Hong Kong University of Science and Technology, The University of Hong Kong, the Taiwan Semiconductor Research Institute and National Taiwan Normal University, turned to an unconventional class of conductors: topological semimetals. Materials such as CoSi host exotic electronic states in which electrons are protected from backscattering by the topology of their band structure. In particular, CoSi possesses long-lived Fermi-arc surface states, chiral electronic pathways that live on the surfaces of the crystal and are remarkably resistant to the scattering that plagues ordinary metals. The researchers reasoned that if these surface states are highly conductive, then making the material thinner, which increases the surface-to-volume ratio, should improve rather than degrade its overall conductivity.

To test this idea, the team grew high-quality single crystals of CoSi and fabricated nanoflakes with thicknesses spanning from one micrometre down to roughly 20 nanometres. The results were unambiguous and, by the standards of conventional metals, almost paradoxical. As the CoSi thickness decreased from 1 micrometre to about 20 nanometres, the resistivity dropped from 7.0 to 0.72 micro-ohm centimetres, a nearly tenfold improvement. The highly conductive surface path, dominated by the topological Fermi-arc states, progressively takes over as the bulk contribution diminishes with thickness. At room temperature, the resistivity of 20-nanometre-thick CoSi is one-tenth that of copper at the same thickness, a margin that could transform the design of the wiring layers in future chips.

Conductivity alone, however, is not enough to qualify a material as an interconnect candidate. Chip wiring must survive brutal operating conditions. Current densities in modern interconnects can exceed millions of amperes per square centimetre, and the resulting momentum transfer from electrons to metal atoms drives electromigration, the gradual transport of atoms that eventually opens voids and breaks the wire. Copper is particularly vulnerable at small dimensions, where grain boundaries and surfaces provide fast diffusion pathways for atoms. The CoSi semimetal, by contrast, is held together by exceptionally strong bonding. The researchers calculated a cohesive energy of 5.4 electronvolts and an atom migration barrier of 3.7 electronvolts, values far higher than those of copper. Experimentally, CoSi nanoflakes maintained reliable conduction at current densities of up to 10^8 amperes per square centimetre and at temperatures up to 450 degrees Celsius, performance that positions the material among the most robust thin-film conductors ever characterized.

The team also verified that CoSi can handle the high-frequency demands of modern communications circuitry. Radiofrequency measurements showed that CoSi interconnects operate cleanly at frequencies up to 40 gigahertz, a regime relevant to wireless transceivers, high-speed data links and advanced processors. Low loss and stable impedance at these frequencies are essential for any material hoping to replace copper in the back-end-of-line metallization of a chip, and the measurements suggest that CoSi’s smooth single-crystalline surfaces and low resistivity translate directly into excellent high-frequency behaviour.

Perhaps most convincingly, the researchers moved beyond isolated test structures and integrated a CoSi interconnect into a functioning silicon circuit. They connected a 16-nanometre-node silicon ring oscillator, a standard benchmark circuit used to evaluate process technology, using CoSi wiring. The oscillator operated at the same frequency as an identical circuit wired with conventional metal interconnects, demonstrating that the exotic semimetal can be married to mainstream silicon manufacturing without degrading circuit performance. This on-chip demonstration is a critical milestone, because many promising nanomaterials have faltered at exactly this step, proving difficult to integrate with the complementary metal-oxide-semiconductor processes that underpin the global electronics industry.

The findings arrive at a moment of intense searching within the semiconductor community. As copper interconnects approach their physical limits, researchers have explored a wide range of alternatives, including graphene, carbon nanotubes and other topological semimetals such as NbAs, NbP and MoP. Recent studies have shown surface-dominated transport in Weyl semimetal nanowires and ultrahigh conductivity in NbAs nanobelts, but questions of manufacturability, reliability and integration have kept any successor to copper out of production. CoSi stands out because it combines several advantages at once: a resistivity that improves with scaling, extraordinary electromigration resistance, thermal stability well beyond typical chip operating temperatures, proven high-frequency performance and demonstrated compatibility with a commercial silicon technology node.

There are, of course, hurdles between a laboratory demonstration and a production line. The CoSi nanoflakes in this study were grown and characterized as single crystals, and future work will need to establish scalable deposition methods, patterning techniques and via integration compatible with high-volume manufacturing. The contact resistance between CoSi and other chip materials, the chemical stability of the semimetal during processing, and the cost of adopting a new metallization scheme all remain open engineering questions. Still, the fundamental physics reported here inverts the central dilemma of interconnect scaling. Instead of fighting a material that gets worse as it gets smaller, chip designers could embrace one that gets better, turning the relentless miniaturization that once threatened copper wiring into an advantage for topological semimetals.

If CoSi and its relatives can clear the remaining manufacturing barriers, the implications extend beyond faster smartphones and data centres. Interconnect resistance is a growing share of the energy budget of modern computing, and taming it would reduce power consumption across everything from cloud servers to edge devices. The work also signals a broader convergence between topological quantum materials and mainstream electronics, a field long dominated by theoretical promise rather than practical devices. With a material that conducts better at 20 nanometres than at a micrometre, survives currents that vaporize copper and runs at 40 gigahertz inside a working silicon chip, the researchers have offered the semiconductor industry a glimpse of what may come after copper, and a reason to believe that the end of transistor scaling is not, after all, the end of computing progress.

Subject of Research: Single-crystalline cobalt silicide (CoSi) semimetal as a highly conductive and reliable nanoscale interconnect material to replace copper in advanced chips

Article Title: Single-crystalline CoSi semimetals with high conductivity and reliability

Article References: Chen, J., Yan, J., Fan, L., Zheng, T., Che, X., Zhu, C., Lu, W., Deng, M., Ng, Y. H., Wang, Z., Wan, Y., Jiang, X., Zhu, Y., Yang, Z., Chen, K. J., Liang, B.-W., Li, K.-S., Lan, Y.-W., Li, L.-J., & Chai, Y. (2026). Single-crystalline CoSi semimetals with high conductivity and reliability. Nature Materials. https://doi.org/10.1038/s41563-026-02740-1

Image Credits: AI Generated

DOI: 10.1038/s41563-026-02740-1

Keywords: CoSi, semimetal, interconnects, copper replacement, topological materials, resistivity scaling, electromigration, nanoelectronics, Fermi arcs, ring oscillator, Nature Materials, chip wiring