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Evidence for unconventional superconductivity in twisted bilayer graphene


The emergence of superconductivity and correlated insulators in magic-angle twisted bilayer graphene (MATBG) has raised the intriguing possibility that its pairing mechanism is distinct from that of conventional superconductors1,2,3,4, as described by the Bardeen–Cooper–Schrieffer (BCS) theory. However, recent studies have shown that superconductivity persists even when Coulomb interactions are partially screened5,6. This suggests that pairing in MATBG might be conventional in nature and a consequence of the large density of states of its flat bands. Here we combine tunnelling and Andreev reflection spectroscopy with a scanning tunnelling microscope to observe several key experimental signatures of unconventional superconductivity in MATBG. We show that the tunnelling spectra below the transition temperature Tc are inconsistent with those of a conventional s-wave superconductor, but rather resemble those of a nodal superconductor with an anisotropic pairing mechanism. We observe a large discrepancy between the tunnelling gap ΔT, which far exceeds the mean-field BCS ratio (with 2ΔT/kBTc ~ 25), and the gap ΔAR extracted from Andreev reflection spectroscopy (2ΔAR/kBTc ~ 6). The tunnelling gap persists even when superconductivity is suppressed, indicating its emergence from a pseudogap phase. Moreover, the pseudogap and superconductivity are both absent when MATBG is aligned with hexagonal boron nitride. These findings and other observations reported here provide a preponderance of evidence for a non-BCS mechanism for superconductivity in MATBG.

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Fig. 1: STS of the tunnelling gap of superconducting MATBG.
Fig. 2: PCS and Andreev reflection for MATBG.
Fig. 3: Tunnelling and Andreev reflection spectra curve fits.
Fig. 4: Pseudogap regime and phase diagram of hole-doped MATBG.
Fig. 5: DT-STS and DT-PCS on non-superconducting MATBG aligned to hBN.

Data availability

The data that support the findings of this study are available at


  1. 1.

    Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).

    ADS  CAS  PubMed  Google Scholar 

  2. 2.

    Yankowitz, M. et al. Tuning superconductivity in twisted bilayer graphene. Science 363, 1059–1064 (2019).

    ADS  CAS  PubMed  Google Scholar 

  3. 3.

    Lu, X. et al. Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene. Nature 574, 653–657 (2019).

    ADS  CAS  PubMed  Google Scholar 

  4. 4.

    Cao, Y. et al. Correlated insulator behaviour at half-filling in magic-angle graphene superlattices. Nature 556, 80–84 (2018).

    ADS  CAS  PubMed  Google Scholar 

  5. 5.

    Saito, Y., Ge, J., Watanabe, K., Taniguchi, T. & Young, A. F. Independent superconductors and correlated insulators in twisted bilayer graphene. Nat. Phys. 16, 926–930 (2020).

    CAS  Google Scholar 

  6. 6.

    Stepanov, P. et al. Untying the insulating and superconducting orders in magic-angle graphene. Nature 583, 375–378 (2020).

    ADS  CAS  PubMed  Google Scholar 

  7. 7.

    Bardeen, J. Electron-phonon interactions and superconductivity. Science 181, 1209–1214 (1973).

    ADS  CAS  PubMed  Google Scholar 

  8. 8.

    Damascelli, A., Hussain, Z. & Shen, Z.-X. Angle-resolved photoemission studies of the cuprate superconductors. Rev. Mod. Phys. 75, 473–541 (2003).

    ADS  CAS  Google Scholar 

  9. 9.

    Fischer, Ø., Kugler, M., Maggio-Aprile, I., Berthod, C. & Renner, C. Scanning tunneling spectroscopy of high-temperature superconductors. Rev. Mod. Phys. 79, 353–419 (2007).

    ADS  CAS  Google Scholar 

  10. 10.

    Isobe, H., Yuan, N. F. Q. & Fu, L. Unconventional superconductivity and density waves in twisted bilayer graphene. Phys. Rev. X 8, 041041 (2018).

    CAS  Google Scholar 

  11. 11.

    Liu, C.-C., Zhang, L.-D., Chen, W.-Q. & Yang, F. Chiral spin density wave and d + id superconductivity in the magic-angle-twisted bilayer graphene. Phys. Rev. Lett. 121, 217001 (2018).

    ADS  CAS  PubMed  Google Scholar 

  12. 12.

    Kennes, D. M., Lischner, J. & Karrasch, C. Strong correlations and d + id superconductivity in twisted bilayer graphene. Phys. Rev. B 98, 241407 (2018).

    ADS  CAS  Google Scholar 

  13. 13.

    Wu, F., MacDonald, A. H. & Martin, I. Theory of phonon-mediated superconductivity in twisted bilayer graphene. Phys. Rev. Lett. 121, 257001 (2018).

    ADS  CAS  PubMed  Google Scholar 

  14. 14.

    Lian, B., Wang, Z. & Bernevig, B. A. Twisted bilayer graphene: a phonon-driven superconductor. Phys. Rev. Lett. 122, 257002 (2019).

    ADS  CAS  PubMed  Google Scholar 

  15. 15.

    Wong, D. et al. A modular ultra-high vacuum millikelvin scanning tunneling microscope. Rev. Sci. Instrum. 91, 023703 (2020).

    ADS  CAS  PubMed  Google Scholar 

  16. 16.

    Kerelsky, A. et al. Maximized electron interactions at the magic angle in twisted bilayer graphene. Nature 572, 95–100 (2019).

    ADS  CAS  PubMed  Google Scholar 

  17. 17.

    Choi, Y. et al. Electronic correlations in twisted bilayer graphene near the magic angle. Nat. Phys. 15, 1174–1180 (2019).

    CAS  Google Scholar 

  18. 18.

    Jiang, Y. et al. Charge order and broken rotational symmetry in magic-angle twisted bilayer graphene. Nature 573, 91–95 (2019).

    ADS  CAS  PubMed  Google Scholar 

  19. 19.

    Xie, Y. et al. Spectroscopic signatures of many-body correlations in magic-angle twisted bilayer graphene. Nature 572, 101–105 (2019).

    ADS  CAS  PubMed  Google Scholar 

  20. 20.

    Wong, D. et al. Cascade of electronic transitions in magic-angle twisted bilayer graphene. Nature 582, 198–202 (2020).

    ADS  CAS  PubMed  Google Scholar 

  21. 21.

    Zondiner, U. et al. Cascade of phase transitions and Dirac revivals in magic-angle graphene. Nature 582, 203–208 (2020).

    ADS  CAS  PubMed  Google Scholar 

  22. 22.

    Nuckolls, K. P. et al. Strongly correlated Chern insulators in magic-angle twisted bilayer graphene. Nature 588, 610–615 (2020).

    ADS  CAS  PubMed  Google Scholar 

  23. 23.

    Choi, Y. et al. Interaction-driven band flattening and correlated phases in twisted bilayer graphene. Nat. Phys. (2021).

  24. 24.

    Saito, Y. et al. Isospin Pomeranchuk effect in twisted bilayer graphene. Nature 592, 220–224 (2021).

    ADS  CAS  PubMed  Google Scholar 

  25. 25.

    Rozen, A. et al. Entropic evidence for a Pomeranchuk effect in magic-angle graphene. Nature 592, 214–219 (2021).

    ADS  CAS  PubMed  Google Scholar 

  26. 26.

    Rodan-Legrain, D. et al. Highly tunable junctions and non-local Josephson effect in magic-angle graphene tunnelling devices. Nat. Nanotechnol. 16, 769–775 16, 769–775 (2021).

  27. 27.

    Deutscher, G. Andreev–Saint-James reflections: a probe of cuprate superconductors. Rev. Mod. Phys. 77, 109–135 (2005).

    ADS  CAS  Google Scholar 

  28. 28.

    Dubouchet, T. et al. Collective energy gap of preformed Cooper pairs in disordered superconductors. Nat. Phys. 15, 233–236 (2019).

    CAS  Google Scholar 

  29. 29.

    Blonder, G. E., Tinkham, M. & Klapwijk, T. M. Transition from metallic to tunneling regimes in superconducting microconstrictions: excess current, charge imbalance, and supercurrent conversion. Phys. Rev. B 25, 4515–4532 (1982).

    ADS  CAS  Google Scholar 

  30. 30.

    Randeria, M., Trivedi, N., Moreo, A. & Scalettar, R. T. Pairing and spin gap in the normal state of short coherence length superconductors. Phys. Rev. Lett. 69, 2001–2004 (1992).

    ADS  CAS  PubMed  Google Scholar 

  31. 31.

    Serlin, M. et al. Intrinsic quantized anomalous Hall effect in a moiré heterostructure. Science 367, 900–903 (2020).

  32. 32.

    Sharpe, A. L. et al. Emergent ferromagnetism near three-quarters filling in twisted bilayer graphene. Science 365, 605–608 (2019).

    ADS  CAS  PubMed  Google Scholar 

  33. 33.

    Hunt, B. et al. Massive Dirac fermions and Hofstadter butterfly in a van der Waals heterostructure. Science 340, 1427–1430 (2013).

    ADS  CAS  PubMed  Google Scholar 

  34. 34.

    Shi, J., Zhu, J. & MacDonald, A. H. Moiré commensurability and the quantum anomalous Hall effect in twisted bilayer graphene on hexagonal boron nitride. Phys. Rev. B 103, 075122 (2021).

    ADS  CAS  Google Scholar 

  35. 35.

    Zhang, Y.-H., Mao, D. & Senthil, T. Twisted bilayer graphene aligned with hexagonal boron nitride: anomalous Hall effect and a lattice model. Phys. Rev. Res. 1, 033126 (2019).

    CAS  Google Scholar 

  36. 36.

    He, M. et al. Symmetry breaking in twisted double bilayer graphene. Nat. Phys. 17, 26–30 (2021).

    CAS  Google Scholar 

  37. 37.

    Khalaf, E., Chatterjee, S., Bultinck, N., Zaletel, M. P. & Vishwanath, A. Charged skyrmions and topological origin of superconductivity in magic-angle graphene. Sci. Adv. 7, eabf5299 (2021).

    ADS  CAS  PubMed  PubMed Central  Google Scholar 

  38. 38.

    Park, J. M., Cao, Y., Watanabe, K., Taniguchi, T. & Jarillo-Herrero, P. Tunable strongly coupled superconductivity in magic-angle twisted trilayer graphene. Nature 590, 249–255 (2021).

    ADS  CAS  PubMed  Google Scholar 

  39. 39.

    Hao, Z. et al. Electric field–tunable superconductivity in alternating-twist magic-angle trilayer graphene. Science 371, 1133–1138 (2021).

    ADS  CAS  PubMed  Google Scholar 

  40. 40.

    Goll, G., Löhneysen, H. V., Yanson, I. K. & Taillefer, L. Anisotropy of point-contact spectra in the heavy-fermion superconductor UPt3. Phys. Rev. Lett. 70, 2008–2011 (1993).

    ADS  CAS  PubMed  Google Scholar 

  41. 41.

    Laube, F., Goll, G., Eschrig, M., Fogelström, M. & Werner, R. Excess current in superconducting Sr2RuO4. Phys. Rev. B 69, 014516 (2004).

    ADS  Google Scholar 

  42. 42.

    Khalaf, E., Bultinck, N., Vishwanath, A. & Zaletel, M. P. Soft modes in magic angle twisted bilayer graphene. Preprint at (2020).

  43. 43.

    Millis, A. J., Sachdev, S. & Varma, C. M. Inelastic scattering and pair breaking in anisotropic and isotropic superconductors. Phys. Rev. B 37, 4975–4986 (1988).

    ADS  CAS  Google Scholar 

  44. 44.

    Zhang, Y. et al. Giant phonon-induced conductance in scanning tunnelling spectroscopy of gate-tunable graphene. Nat. Phys. 4, 627–630 (2008).

    CAS  Google Scholar 

  45. 45.

    Hapala, P. et al. Mechanism of high-resolution STM/AFM imaging with functionalized tips. Phys. Rev. B 90, 085421 (2014).

    ADS  CAS  Google Scholar 

  46. 46.

    Stroscio, J. A. & Celotta, R. J. Controlling the dynamics of a single atom in lateral atom manipulation. Science 306, 242–247 (2004).

    ADS  CAS  PubMed  Google Scholar 

  47. 47.

    Wolter, B. et al. Spin friction observed on the atomic scale. Phys. Rev. Lett. 109, 116102 (2012).

    ADS  PubMed  Google Scholar 

  48. 48.

    Daghero, D. & Gonnelli, R. S. Probing multiband superconductivity by point-contact spectroscopy. Supercond. Sci. Technol. 23, 043001 (2010).

    ADS  Google Scholar 

  49. 49.

    Kim, K. et al. Van der Waals heterostructures with high accuracy rotational alignment. Nano Lett. 16, 1989–1995 (2016).

    ADS  CAS  PubMed  Google Scholar 

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We thank P. Jarillo-Herrero, A. H. MacDonald and S. A. Kivelson for helpful discussions. We thank C.-L. Chiu, G. Farahi and H. Ding for helpful technical discussions. This work was primarily supported by the Gordon and Betty Moore Foundation’s EPiQS initiative grant GBMF9469 and DOE-BES grant DE-FG02-07ER46419 to A.Y. Other support for the experimental work was provided by NSF-MRSEC through the Princeton Center for Complex Materials NSF-DMR- 2011750 and NSF-DMR-1904442, ExxonMobil through the Andlinger Center for Energy and the Environment at Princeton, and the Princeton Catalysis Initiative. A.Y. acknowledges the hospitality of the Aspen Center for Physics, which is supported by the National Science Foundation grant PHY-1607611, and Trinity College, Cambridge, UK, where part of this work was carried out with the support of, in part, a QuantEmX grant from ICAM and the Gordon and Betty Moore Foundation through the grant GBMF9616. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, grant JPMXP0112101001, and JSPS KAKENHI grants 19H05790 and JP20H00354.

Author information




M.O., K.P.N., D.W. and A.Y. designed the experiment. M.O., D.W. and K.P.N. fabricated the devices used for the study. M.O., K.P.N., D.W. and R.L.L. carried out STM/STS and PCS measurements, with invaluable input from X.L. on the latter. M.O., D.W. and K.P.N. performed the data analysis. K.W. and T.T. synthesized the hBN crystals. All authors discussed the results and contributed to the writing of the manuscript.

Corresponding author

Correspondence to Ali Yazdani.

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The authors declare no competing interests.

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Peer review information Nature thanks Dante Kennes and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

This file contains Supplementary Sections A–L, including text and data, tables and Supplementary Figs. 1–16. See contents page for details.

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Oh, M., Nuckolls, K.P., Wong, D. et al. Evidence for unconventional superconductivity in twisted bilayer graphene. Nature (2021).

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