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Nodeless electron pairing in CsV3Sb5-derived kagome superconductors


The newly discovered kagome superconductors represent a promising platform for investigating the interplay between band topology, electronic order and lattice geometry1,2,3,4,5,6,7,8,9. Despite extensive research efforts on this system, the nature of the superconducting ground state remains elusive10,11,12,13,14,15,16,17. In particular, consensus on the electron pairing symmetry has not been achieved so far18,19,20, in part owing to the lack of a momentum-resolved measurement of the superconducting gap structure. Here we report the direct observation of a nodeless, nearly isotropic and orbital-independent superconducting gap in the momentum space of two exemplary CsV3Sb5-derived kagome superconductors—Cs(V0.93Nb0.07)3Sb5 and Cs(V0.86Ta0.14)3Sb5—using ultrahigh-resolution and low-temperature angle-resolved photoemission spectroscopy. Remarkably, such a gap structure is robust to the appearance or absence of charge order in the normal state, tuned by isovalent Nb/Ta substitutions of V. Our comprehensive characterizations of the superconducting gap provide indispensable information on the electron pairing symmetry of kagome superconductors, and advance our understanding of the superconductivity and intertwined electronic orders in quantum materials.

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Fig. 1: Evolution of CDW and superconductivity in CsV3Sb5 on chemical substitution.
Fig. 2: Isotropic superconducting gap in Cs(V0.86Ta0.14)3Sb5.
Fig. 3: Isotropic superconducting gap in charge-ordered Cs(V0.93Nb0.07)3Sb5.
Fig. 4: Robust isotropic SC gap on suppression of CDW.

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Data availability

Data are available from the corresponding author upon reasonable request.


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We thank W. Zhang, S. Huh and M. Liu for stimulating discussions. This work was supported by the National Key Research and Development Program of China (grant nos 2020YFA0308800 and 2022YFA1403400), the Grants-in-Aid for Scientific Research (KAKENHI) (grant nos JP18K13498, JP19H01818, JP19H00651 and JP21H04439) from the Japan Society for the Promotion of Science (JSPS), JSPS KAKENHI on Innovative Areas ‘Quantum Liquid Crystals’ (grant no. JP19H05826), the Center of Innovation Program from the Japan Science and Technology Agency (JST) and MEXT Quantum Leap Flagship Program of Japan (MEXT Q-LEAP) (grant no. JPMXS0118068681), the National Science Foundation of China (grant nos 12061131002, 12234003 and 92065109),. and the Beijing Natural Science Foundation (grant nos Z210006 and Z190006). X.S. was supported by the Beijing Institute of Technology (BIT) Research Fund Program for Young Scholars. Z.W. thanks the Analysis and Testing Center at BIT for assistance in facility support. J.-X.Y. was supported by South University of Science and Technology of China principal research grant (no. Y01202500). X.H. acknowledges the support from the China Postdoctoral Science Foundation Fellowship (no. 2022M723112). J.H. was supported by the Ministry of Science and Technology of China (grant no. 2022YFA1403901) and the National Natural Science Foundation of China (grant no. NSFC-1188810).

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Authors and Affiliations



Y.Z., X.S. and K.O. conceived the project. Y.Z. performed the ARPES experiments with assistance from A.M., S.N., T.S. and K.L., and with guidance from T.K. and K.O. Z.G., J.-X.Y., D.D., C.M.III, R.K. and H.L. contributed to interpretation of data and making a conclusion. J.L., Y.L. and Z.W. grew the samples and performed sample characterizations. X.W. performed the band calculations. X.W., X.H. and J.H. contributed to theoretical inputs. Y.Z., X.S., X.W., J.-X.Y. and K.O. prepared the manuscript with input from all authors.

Corresponding authors

Correspondence to Zhiwei Wang, Xun Shi or Kozo Okazaki.

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Extended data figures and tables

Extended Data Fig. 1 Fermi surface evolution upon Nb/V substitutions.

a–c, Fermi surface maps integrated over EF ± 5 meV for the pristine, 7%-Nb and 14%-Ta substituted CsV3Sb5 samples, respectively. The spectra were measured with He Iα photons (hν = 21.218 eV) at T = 7 K. d, Line cuts along kx = 0. The black lines are the Lorentizen fits to determine the kF positions. e, Summary of the kF evolution of three Fermi surfaces upon Nb/V substitutions. The error bars represent the uncertainties of the fits.

Extended Data Fig. 2 Fermi surfaces of all measured Ta0.14 samples.

a–d, ARPES intensity integrated over EF ± 5 meV. e–h, kF points at which the superconducting gap is measured.

Extended Data Fig. 3 Fermi surfaces of all measured Nb0.07 samples.

a–d, ARPES intensity integrated over EF ± 5 meV. e–h, kF points at which the superconducting gap is measured.

Extended Data Fig. 4 Superconducting gap at different kz for the Cs(V0.93Nb0.07)3Sb5 sample.

a, FS map taken with 5.8-eV laser. b, EDCs at kF marked in a. The black lines are the fits of these EDCs. c, Symmetrized EDCs for b. d–f, Same as a-c but for the data taken with 7-eV laser. The curves are vertically offset for clarity. g. Comparison of the SC gap amplitude measured with 5.8-eV and 7-eV laser. The inset shows the kz positions corresponding to these two photon energies.

Extended Data Fig. 5 X-ray diffraction (XRD) measurements.

a, XRD of the pristine CsV3Sb5, Nb0.07 and Ta0.14 single crystals. b, Extracted in-plane lattice constants for these three single crystals.

Extended Data Fig. 6 Spectral evidence of the electron-phonon coupling.

a–c, ARPES intensity plots of the α and β bands nearly along Γ−Κ direction for the pristine CsV3Sb5, Nb0.07 and Ta0.14 samples, respectively. These ARPES data are taken with 7-eV laser at T = 6 K. d–f, Extracted band dispersions. a and d are adopted from the ref. 38, in which the Tc of the measured CsV3Sb5 is approximately 2.5 K. g, Ratio between the velocity of the bare band and the Fermi velocity for the pristine, Nb0.07 and Ta0.14 samples, plotted as a function of their Tc.

Extended Data Fig. 7 Comparison of the van Hove singularities.

a–c, ARPES intensity plots along K-M-K direction for pristine, 7%-Nb and 14%-Ta substituted CsV3Sb5, respectively. These ARPES measurements were performed using a photon energy hν = 21.218 eV (He Iα). d–e, Curvature plots of a–c near EF in energy and around M point in momentum. g, EDCs extracted at M point. The arrows mark the peak positions of these EDCs. h, Band dispersion around M point extracted from the curvature plots.

Extended Data Fig. 8 Calculated band structures for the CsV3Sb5, Cs(V0.93Nb0.07)3Sb5 and Cs(V0.86Ta0.14)3Sb5 samples based on density functional theory.

The experimentally determined lattice constants are used in the calculation.

Extended Data Table 1 Statistics of the SC gap for the Ta0.14 samples with Tc ≈ 5.2 K
Extended Data Table 2 Statistics of the SC gap for the Nb0.07 samples with Tc ≈ 4.4 K

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Zhong, Y., Liu, J., Wu, X. et al. Nodeless electron pairing in CsV3Sb5-derived kagome superconductors. Nature 617, 488–492 (2023).

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