Guguchia, Z.Mielke, C.Das, D.Gupta, R.Yin, J.-X.Liu, H.Yin, Q.Christensen, M.H.Tu, Z.Gong, C.Shumiya, N.Hossain, Md ShafayatGamsakhurdashvili, TsElender, M.Dai, PengchengAmato, A.Shi, Y.Lei, H.C.Fernandes, R.M.Hasan, M.Z.Luetkens, H.Khasanov, R.2023-01-272023-01-272023Guguchia, Z., Mielke, C., Das, D., et al.. "Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5." <i>Nature Communications,</i> 14, (2023) Springer Nature: https://doi.org/10.1038/s41467-022-35718-z.https://hdl.handle.net/1911/114294Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals AV3Sb5, key spectroscopic evidence has remained elusive. Here we utilize pressure-tuned and ultra-low temperature muon spin spectroscopy to uncover the unconventional nature of superconductivity in RbV3Sb5 and KV3Sb5. At ambient pressure, we observed time-reversal symmetry breaking charge order below $${T}_{{{{{{{{\rm{1}}}}}}}}}^{*}\simeq$$110 K in RbV3Sb5 with an additional transition at $${T}_{{{{{{{{\rm{2}}}}}}}}}^{*}\simeq$$50 K. Remarkably, the superconducting state displays a nodal energy gap and a reduced superfluid density, which can be attributed to the competition with the charge order. Upon applying pressure, the charge-order transitions are suppressed, the superfluid density increases, and the superconducting state progressively evolves from nodal to nodeless. Once optimal superconductivity is achieved, we find a superconducting pairing state that is not only fully gapped, but also spontaneously breaks time-reversal symmetry. Our results point to unprecedented tunable nodal kagome superconductivity competing with time-reversal symmetry-breaking charge order and offer unique insights into the nature of the pairing state.engThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.Journal articles41467-022-35718-zhttps://doi.org/10.1038/s41467-022-35718-z