Orbital-hybridization-induced Ising-type superconductivity in a confined gallium layer

Nature Materials (2026)Cite this article In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper-pair wavefunctions and give rise to unconventional superconducting states. Here we use plasma-free confinement epitaxy assisted by a carbon buffer layer to synthesize a gallium trilayer sandwiched between graphene and a 6H-SiC(0001) substrate. Within this confined gallium layer, we demonstrate interfacial Ising-type superconductivity driven by atomic orbital hybridization. Electrical transport measurements reveal that the in-plane upper critical magnetic field reaches ~21.98 T at T = 400 mK, approximately 3.38 times the Pauli paramagnetic limit. Angle-resolved photoemission spectroscopy measurements, combined with theoretical calculations, confirm the presence of split Fermi surfaces with Ising-type spin textures at the K and K′ valleys of the confined gallium layer, originating from strong hybridization with the SiC substrate. This work establishes a strategy for realizing unconventional pairing wavefunctions through the synergistic combination of quantum confinement and interfacial hybridization effects.This is a preview of subscription content, access via your institution Access Nature and 54 other Nature Portfolio journals Get Nature+, our best-value online-access subscription $32.99 / 30 days cancel any timeSubscribe to this journal Receive 12 print issues and online access $259.00 per yearonly $21.58 per issueBuy this articleUSD 39.95Prices may be subject to local taxes which are calculated during checkoutThe data that support the findings of this Article are available via Zenodo (https://doi.org/10.5281/zenodo.18795669)54.Reyren, N. et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007).Article CAS PubMed Google Scholar Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. 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The STM/STS measurements are partially supported by an NSF CAREER award (DMR-1847811) and an NSF grant (DMR-2241327). The in-house ARPES measurements were performed in the NSF-supported 2DCC MIP facility (DMR-2039351). C.-Z.C. acknowledges support from the Gordon and Betty Moore Foundation’s EPiQS Initiative (GBMF9063 to C.-Z.C.). The work done at the National High Magnetic Field Laboratory is supported by NSF Cooperative Agreement number DMR-2128556 and the State of Florida. H.Y. acknowledges the Shanghai Pujiang Program (24PJA062) and an NSFC grant (12574146). Y.C. acknowledges the Diamond Light Source for time on beamline I09 under proposal number NT37930. We acknowledge the MAX IV Laboratory for beamtime on the BLOCH beamline under proposal numbers 20230668 and 20240633. Research conducted at MAX IV, a Swedish national user facility, is supported by Vetenskapsrådet (Swedish Research Council, VR) under contract number 2018-07152, Vinnova (Swedish Governmental Agency for Innovation Systems) under contract number 2018-04969 and Formas under contract number 2019-02496. Y.W. acknowledges support from UNT startup funds and NSF Grant No. DMR-2340733, as well as computational resources provided by the Texas Advanced Computing Center (Lonestar6).These authors contributed equally: Hemian Yi, Yunzhe Liu, Chengye Dong, Yiheng Yang.Department of Physics, The Pennsylvania State University, University Park, PA, USAHemian Yi, Yunzhe Liu, Zi-Jie Yan, Zihao Wang, Lingjie Zhou, Stephen Paolini, Bing Xia, Bomin Zhang, Xiaoda Liu, Hongtao Rong, Annie G. Wang, Saswata Mandal, Kaijie Yang, Benjamin N. Katz, Vincent H. Crespi, Joshua A. Robinson, Chao-Xing Liu & Cui-Zu ChangTsung-Dao Lee Institute and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, ChinaHemian YiDepartment of Materials Science and Engineering and Two-dimensional Crystal Consortium, The Pennsylvania State University, University Park, PA, USAChengye Dong & Joshua A. RobinsonDepartment of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford, UKYiheng Yang, Dingsong Wu, Houke Chen, Jieyi Liu & Yulin ChenCenter for Correlated Matter and School of Physics, Zhejiang University, Hangzhou, ChinaLunhui HuDiamond Light Source, Harwell Science and Innovation Campus, Didcot, UKJieyi Liu & Tien-Lin LeeDepartment of Physics, University of North Texas, Denton, TX, USAYuanxi WangSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarSearch author on:PubMed Google ScholarH.Y. and C.-Z.C. conceived and designed the experiment. H.Y., Z.-J.Y., L.Z. and C.-Z.C. conducted the electrical transport measurements. H.Y., H.R. and C.-Z.C. performed the in-house ARPES measurements. Y.Y., D.W., H.C. and Y.C. performed the synchrotron ARPES measurements. Y.Y., J.L. and T.-L.L. performed the X-ray standing-wave measurements. C.D. and J.A.R. synthesized all the samples and performed the STEM, XPS and Raman measurements. Z.W., S.P., B.X. and C.-Z.C. performed the STM/STS measurements. L.Z., B.Z. and X.L. performed the electrical transport measurements in a dilution refrigerator. Y.L., S.M., K.Y., B.N.K., L.H., V.H.C., Y.W. and C.-X.L. provided theoretical support. H.Y., Y.L., Y.W., C.-X.L. and C.-Z.C. analysed the data and wrote the manuscript, with input from all authors.Correspondence to Hemian Yi, Chao-Xing Liu or Cui-Zu Chang.The authors declare no competing interests.Nature Materials thanks the anonymous reviewers for their contribution to the peer review of this work. Peer reviewer reports are available.Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.a, Schematic of the Ga intercalation process in a SiC substrate with a surface of ~90% monolayer graphene/buffer regions and ~10% buffer-only regions. b, c, XPS spectra of C 1 s before (b) and after (c) the Ga intercalation process. The P1 and P2 components in the C 1 s spectra of partially epitaxial graphene disappear after the Ga intercalation, indicating decoupling of the buffer layer from the SiC substrate. d, XPS spectra of Ga 3 d after the Ga intercalation process. The monolayer graphene forms when the ~10% buffer-only region decouples from the SiC substrate during Ga intercalation.a, STEM image of a graphene/trilayer Ga/SiC heterostructure. b-d, The corresponding EDS maps of Ga (b), Si (c), and C (d).The blue and red dots correspond to the normalized Si 2 s photoelectron yield and the (0006) Bragg reflectivity of the 6H-SiC(0001) substrate, respectively. Since the SiC lattice is used to generate X-ray standing waves, the coherent fraction f0006 = 1 is expected for the Si 2 s peak, with a polarization factor P0006 = 1. In our experiment, the measured f0006 = 1.02 and P0006 = 1.01 confirm the reliability of our X-ray standing wave measurements.a, Raman spectra of bilayer graphene/trilayer Ga/SiC, monolayer graphene/SiC, monolayer graphene/trilayer Ga/SiC, and carbon buffer/SiC, respectively. b, Optical microscopy image of a graphene/trilayer Ga/SiC sandwich. c, Raman spectra of the graphene/trilayer Ga/SiC sandwiches exhibit two low-frequency metal modes at 25 cm⁻¹ and 53 cm⁻¹. The R1 and R2 peaks emerge only after Ga intercalation, confirming their origin in the trilayer Ga layer. d, Raman map of the R1 peak at 25 cm−1 over a 20 ×20 μm2 aera, as marked in (b).a, Large-scale STM image of a graphene/trilayer Ga/SiC heterostructure (VB = +100 mV, It = 100 pA, and T = 310 mK). b, c, Temperature-dependent dI/dV spectra of monolayer graphene/trilayer Ga/SiC (b) and bilayer graphene/trilayer Ga/SiC (c) heterostructures (VB = +1.5 mV, It = 500 pA, and T = 310 mK). The data in (b, c) are measured in regions A and B in (a), respectively.a, Band structures of trilayer Ga/SiC with three different structural orientations. b, Band structures of bilayer Ga/SiC. The red squares and the black curves represent the band structures obtained using maximally localized Wannier functions (MLWF) and first-principles calculations, respectively.a, STEM image of a graphene/trilayer Ga/SiC sandwich. b, Enlarged STEM image of the area in (a). c, Integrated intensity along the perpendicular direction. The spacing between the bottom two Ga layers is d1 = 0.22 nm, while the spacing between the top two Ga layers is d2 = 0.26 nm. The analysis of Fig.1b gives comparable values, with d1 = 0.21 nm and d2 = 0.27 nm, respectively.a, b, Spin textures of bilayer Ga showing the Sz component for spin-down (a) and spin-up (b) states. c, Spin polarization with the Sx, Sy, and Sz components.a, R-T curves of Sample S1 under varying μ0H||. b, R-μ0H curves of Sample S1 measured under μ0H|| at different temperatures. c, Temperature dependence of μ0Hc2,||. All data points in (c) are extracted from (a) and (b). d-f, Same as (a-c), but on Sample S4. All data points in (f) are extracted from (d) and (e). The fitting parameters in (c) and (f) are adopted from those in Fig. 4c (Δ1 = 28 meV and 1/τ ≈ 18.1 meV).a, Calculated μ0Hc2,||/μ0Hp - T/Tc with varying impurity scattering strength 1/τ. The strength of Rashba- and Ising-type SOC are fixed at \({\Lambda }_{f}=10\) meV and Δ1 = 0 meV, respectively. b, Calculated μ0Hc2,||/μ0Hp - T/Tc with Δ1 = 28 meV. \({\Lambda }_{f}\) and 1/τ are varied.Supplementary Texts 1–9, Figs. 1–20 and references.Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.Reprints and permissionsYi, H., Liu, Y., Dong, C. et al. Orbital-hybridization-induced Ising-type superconductivity in a confined gallium layer. Nat. Mater. (2026). https://doi.org/10.1038/s41563-026-02573-yDownload citationReceived: 17 August 2025Accepted: 09 March 2026Published: 13 April 2026Version of record: 13 April 2026DOI: https://doi.org/10.1038/s41563-026-02573-yAnyone you share the following link with will be able to read this content:Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative